Prologue to the First Question
1.Pr.1 On the Kinds of Proof
‘Proof’ is said in many ways.
(1) All knowledge, properly speaking, is the knowledge of a knower, and therefore in the formal and proper sense a proof is that inference of a knower that actually results in knowledge of some kind.
(2) However, in a broader and commonly used sense, we take proofs to be a logical object, a template formed by reason, and having existence only in reason, which serves to guide and communicate this kind of inference. This being-of-reason is distinct from the inference itself but drawn from it. In the first sense it is possible to say honestly that you have no proof of something when you have in hand a proof in the second sense; that is to say, having the template or model for inference is not on its own sufficient for inferring in the way it would indicate. This can happen, for instance, if someone explains an inference, and you understand their explanation, but you disagree with the premise; in this case, you cannot apply the premise to your starting point. Another kind of situation in which it can happen is when you are considering the inference hypothetically in order to determine whether it is a proof.
(3) In an even broader sense, and slightly improper, we use the term 'proof' to indicate a set of logically connected set of statements that are spoken or written. In the template sense, a proof is the same regardless of language, but in this sense a proof changes depending on the language in which it is couched, because it is in reality a linguistic product of the liberal arts of logic, grammar, and rhetoric in order to communicate the template.
(4) And in another sense, we call 'proof' things that are neither inferences nor ways of communicating them, but are instead real things or experiences that allow for inferences productive of knowledge. In this case there can be a proof of something but nobody knows it; that is to say, the evidence is available but is not recognized as such.
In what follows, the first sense of proof is used, although everything said about proof in this sense is easily transferred, with only minor modification, to proof in the second sense. Even in only the first and most proper of these senses, 'proof' is said in many ways, some more proper than others.
Aristotle tells us that a deduction (syllogismos) is reasoning (logos) in which, supposing some things, other things necessarily follow because of them. This reasoning occurs by way of a middle term, or medium of inference, which establishes the consequence and is closely linked with the questions we ask in order to know. If I ask whether a star is a dwarf star, this can be seen as asking whether there is something from which we can get a middle term, or perhaps a series of middle terms linked deductively, that connects being a dwarf star to anything we already know. If I ask whether a thing exists, this can be seen as asking whether there is something from which we can get middle terms from which its existence follows.
We regard ourselves as having unqualified knowledge of a thing when we think we know the why of a thing, precisely as it is, so that we understand that it must be so. A demonstration (apodeixis), which literally means a 'manifestation' or a 'showing forth', is a deductive inference productive of such knowledge in the sense that genuinely understanding the inference is itself the knowledge, where the principles of the inference are already understood. It is thus the most perfect answer to a question about why something exists or is as it is. For a deductive inference to be demonstrative, certain conditions must obtain.
(1) Its principles must be neither merely probable, nor doubtful, nor false, but true. What is known is always known only insofar as it is linked to being; even negations, privations, fictions, and so forth, can only be known insofar as we can connect them to what is. For instance, a hole is known only insofar as it can be related either to what is removed from something that actually is, such as the dirt removed from dirt to make a hole in the ground or to what is that can be related to it, such as its walls or something that could pass through it. But being and truth are convertible terms, so things can be known only insofar as they are linked to what is true.
(2) These principles must be reducible to first principles or else be first principles themselves, and these first principles must be immediate, in the sense that no middle term is required to join subject and predicate. That is, if you understand the subject term and the predicate term, you understand that the predicate term applies to the subject term without some further term through which it is applied. Such premises are necessary in some way, and are known by understanding (intelligentia, noesis), which is higher than the kind of knowledge given by demonstration (which is scientia, episteme).
A demonstrative proof is always a proof of a conclusion, which says something about something in some way. If there were an infinite regress in demonstration, there would be nothing about which something is said, or else nothing to say about it, because there would only be an endless series of middle terms connected with only one of these. Moreover, a series of middle terms can be treated as a single, complex middle term; in an infinite regress, all the terms other than one would be a middle term, which would not be mediating. Therefore, there must be principles that are immediate.
(3) The principles must be prior, that is, better known than the conclusion and knowable independently of the conclusion; and the conclusion must actually follow from the principles. The 'better' here indicates a kind of priority. One thing can be better known than another in two different ways: one, properly and in an unqualified way, in which it is better known in itself or by nature, because it is logically or intelligibly prior or more fundamental; the other, in a qualified way, in which it is the thing we happen to have come to know earlier. The first kind is more fundamental.
In a circular deduction, something is treated as both principle and conclusion; but demonstration must be of posterior, lesser known conclusions from prior, better known principles, which cannot be if conclusion and principle are the same, for nothing can be both prior and posterior with respect to one and the same thing, and nothing that is the same thing can be both better known and lesser known at the same time. Further, if demonstrations could be circular, we could prove things simply through themselves: As this is so, it is so. No knowledge can be produced by a such an argument, since it treats conclusions as if they were first principles in need of nothing beyond themselves.
Thus demonstrative proof is when a conclusion must follow from known necessary truths, so that it is known to be true because of them. It is a serious error to assume that this can be done only in one way. There are many variations on how this can happen, some of which are more perfectly demonstrative than others.
(1) Direct demonstration can be had in two forms. One is from what is prior absolutely and in itself, the underlying principles that make something so, and is called demonstration propter quid, sometimes called 'demonstration of reasoned fact' or (using Greek rather than Latin) 'demonstration dioti'. If we focus on the conclusion, a demonstration propter quid shows why the predicate must go with the subject; it identifies a cause or reason insofar as it requires something so that it cannot be otherwise. In many cases, it shows that a cause requires an effect.
(2) The other form of direct demonstration is through what is prior relative to us, and is called demonstration quia, or sometimes 'demonstration of fact' or (using Greek) 'demonstration hoti'. It does not give an underlying account showing why the predicate in the conclusion must go with subject; it merely establishes, on the basis of something we know, that it does. In many cases, it shows that an effect requires a cause, or a sign something that it signifies. A quia demonstration differs from a propter quid demonstration in that its middle term, the link allowing the inference, is not a proper cause. But there are two other things it could be. It could be a remote cause, and then we have what is sometimes called an a priori quia demonstration. It could also be an effect, in which case we have what is sometimes called an a posteriori quia demonstration.
Demonstration quia is especially important in subalternate sciences; in such cases the higher science will sometimes have demonstrations propter quid but the subalternate sciences have demonstrations quia for the same conclusions. We see this in an especially easy way in the application of mathematics to the natural world; the physicist may show that some effect is due to a mathematical property, whereas the mathematician may show why it is.
We see similarly that there are situations in which one can join demonstration quia and demonstration propter quid so that by demonstration quia we move from effect to cause and by demonstration propter quid we move from cause to effect, thus first establishing the cause from the effect and then establishing how the cause makes the effect to be. This is not circular demonstration, because (1) in moving from effect to cause and then cause to effect, we are doing so in different ways and (2) to conjoin the two kinds of demonstration requires an additional investigation of different facts, evidences, and possibilities. When we have this kind of demonstration, it is known as a demonstrative regress or regressus. Jacopo Zabarella, who is most associated with discussion of this kind of demonstration, identifies the stages of the regress as resolution (demonstration quia from effect to cause), mental examination, which others call intellectual negotiation (investigation of different possible ways the cause might cause the effect), and composition (demonstration propter quid from cause to effect).*
(3) Indirect demonstration shows something impossible by reducing it to a better known impossibility, and this is often called reductio ad absurdum.
(4) In other situations, we demonstrate only on a presupposition about an effect or something similar. Thus, for instance, we might prove a conclusion about a system on the supposition that it is not interfered with from outside; this is not itself something that is properly necessary, but the conclusion will necessarily apply to any situation in which it has conditional necessity, that is, any situation in which it is in fact true. This kind of conditional demonstration is sometimes called demonstration ex suppositione; it can be considered a demonstration in which our starting points are necessary in a qualified rather than full sense.
(5) Sometimes we have something that could be called a demonstration, but for which the principles are 'better known' in a secondary way. That is, they might be better known not in themselves but to particular people, in that they happened to learn them earlier. This can be called relative demonstration, although one sometimes also finds it called 'demonstration ad hominem'. In this form of demonstration the conclusion is aimed at and achieved only obliquely; what is demonstrated, strictly speaking, is the connection between the conclusion and what is already known to some particular person.
(6) At times our principles bring us to a conclusion that is true but only in a qualified way. For instance, we may be able to demonstrate that something is true to a certain degree of approximation; this demonstration of approximate truth is common when we are working with abstract idealizations or are ignoring factors minor enough to be negligible.
(7) Another way in which we can come to a conclusion that is true but only in a qualified way is when we are able to establish that something is truth-like or is congruous, fitting, or appropriate given what is true. This kind of demonstration is often called demonstration ex convenientia.
(8) Perhaps we can also put here what is often called a moral demonstration, in which we proceed to a conclusion that is known in a qualified sense, in that we know it not directly (scientia, episteme) but in the sense of being able to act prudently or with skill on it.
Of all of these, demonstration propter quid is most properly called demonstration, because it meets the requirements for demonstration without qualification and simply. Demonstration quia and reductio ad absurdum, on the other hand, do so indirectly. Both are much more common than propter quid demonstration. All of the others, which may occur in either direct or indirect forms, are demonstration with various qualifications; they may be considered imperfect as demonstrations, but granted the relevant qualifications would fit the definition of demonstration, so are at least in the same family.
Besides demonstration, which is proof in the strictest sense, there are kinds of argument that are called proof in a looser sense, because they provide stable reasoned opinions that help in disposing us to knowledge. These are known as dialectical proofs. They proceed from what are generally called 'probable premises', but 'probable' here is to be understood in the sense that they are accepted either by the wise (that is, those who are in a position to know) or by the many (that is, reasonable persons in general, abstracting from individual peculiarities), or that they are similar to such things as are accepted by the wise or many.
While dialectical propositions are lacking with respect to something required for demonstration, nonetheless arguments based upon them are often fittingly regarded as proofs in a looser sense of the term. They all are deductive in some way, and thus have a structure in which, some things being supposed, some things must follow; the connection between the two is given its force by something already known, which is presupposed, either explicitly or implicitly, as guiding the argument. This is what is known as a maximal proposition, a topic, or a commonplace. It is, so to speak, that on whose stability the argument stands. General examples might be 'What pertains to the more general, pertains to the more specific' or 'Things whose definitions are different are themselves different', but specific fields can have analogous propositions appropriate to their specific material, like conservation laws used to solve particular problems in physics and chemistry or general rules of evidence applied to particular cases in law. Such propositions serve as rules or guidelines by which we keep on track in using probable premises; they are also how we sort through various possibilities in order to find good arguments. In addition to such rules, we also may make suppositions or hypotheses, in order to see where they would end up, and postulates, by which we simplify complex problems into simpler ones. Because of this, dialectical reasoning that is well done often approaches demonstration; likewise, it may help us to rule out possibilities until we are in a position to demonstrate, as happens in the negotiation or examination stage of the demonstrative regress. However, unlike demonstrative proofs, nothing prevents dialectical proofs from being circular, and it is possible to have a dialectical proof from something less known to something more known, because coherence and practical value are much more important for dialectical reasoning than for demonstrative reasoning.
Outside of dialectic, we sometimes use the term 'proof' of arguments that get their primary force from rhetorical or poetic grounds, which become relevant whenever we are communicating arguments. All arguments, demonstrative, dialectical, or otherwise, have rhetorical aspects concerned with practical pursuit or avoidance of good and bad things and poetic aspects concerned with plausibility in imaginative representation, but in some arguments rhetorical or poetic presentation is itself the means by which we get from the principles to the conclusions. For instance, a rhetorically forceful argument might get its force from the fact that the one who presents it comes across as an honest, competent, and sincere fellow or as a credentialed expert (ethos) or from the fact that the conclusion appeals extremely well to the passions of the one to whom it is presented (pathos). Likewise, it sometimes happens that the conclusion seems to follow because the argument is presented in a way that so appeals to our imagination that we seem almost to see the conclusion to be so, due to the vividness with which it contributes to our imagination, as in a very cleverly done thought experiment. These kinds of plausibility-based arguments are called 'proofs' when they have effects like those of proofs; as 'proof' here is a kind of metaphor indicating a particular kind of effect of the argument rather than its very nature, all of these arguments are proofs only figuratively. We should, however, not confuse them with sophisms, which we do sometimes call 'sophistical proofs'; this use of the term is not a metaphor but abusive, as if we said, 'alleged proofs' or 'proofs so-called'. Sophisms only have value for knowledge in being refuted. Rhetorical and poetic proofs, on the other hand, have a genuine contribution to play, despite not themselves bringing about knowledge; they smooth the communication of arguments, guide us in taking them into account in our practical lives, and they can even sometimes help us to form dialectical arguments by making it easier to consider possibilities, formulate middle terms, or avoid certain errors.
The First Vatican Council says, quoting Romans 1:20, The same holy mother church holds and teaches that God, the source and end of all things, can be known with certainty from the consideration of created things, by the natural power of human reason: ever since the creation of the world, his invisible nature has been clearly perceived in the things that have been made. If we are interested in discussing divine things so as to know them, therefore, it is often of interest to determine with what kind of proofs we are working, particularly in order to identify the manner in which we know and the limitations thereof. The most important question touching on this is whether anything can be demonstrated, or whether we are confined to dialectical proofs.
1.Pr.2 On the Demonstrability of Something Divine
Let us consider the question of whether it is demonstrable that there is something divine of some kind. The demonstrability of the existence of something divine might be rejected for two reasons.
(1) One might oppose it by claiming that the existence of divine things is grasped immediately by understanding or intelligence. This makes the existence of divine things a first principle; first principles are indemonstrable because any demonstration presupposes them. First principles are in some sense known, but are not known by demonstration; indeed, they are already more known than any proof you could give. There are two major grounds on which one might make this claim.
(1.1) One might make the claim that enunciable propositions like “The divine exists” or “God exists” are known immediately upon proper understanding of their terms.
(1.2) One might make the claim that the divine itself is an immediate object of the intellect, prior to any candidate for a starting-point from which the existence of the divine may be proven.
It is important to note with regard to both claims that this position does not require us to say that there are no arguments for God's existence, only that if there are any, they fail in one crucial feature essential to demonstration as such: that it proceeds from the more known to the less known, or from the prior in knowledge to the posterior. In the same way we can have no demonstrations for the principle of noncontradiction, because it is at least as known as, or better known than, anything from which one could try to demonstrate it. Nonetheless, we can have arguments for the principle of noncontradiction, for instance, arguments by retorsion, showing that people who profess to deny it nonetheless accept it, or arguments by consensus gentium, or arguments showing its connection with other fundamental principles. We could thus still have additional dialectical arguments for God's existence, even if either of the above claims were true. If, however, God's existence is already known by immediate understanding, then in taking it as a conclusion, there is no argument we could make that would proceed from something prior to and better known than the conclusion, and thus no way we could demonstrate the conclusion. Nonetheless, there is reason to reject either of these.
(1.1) With regard to the first, which holds that at least some enunciable propositions about God's existence are known when their terms are known, without the mediation of any middle term. Of this position, St. Thomas gives two explanations (SCG 1.11.1): This partly arises from the custom by which from the beginning people are brought up to hear and to call upon the name of God, and This partly comes about because of a failure to distinguish between what is known per se, simply speaking, and what is known per se by us. Thus the position underestimates the extent to which the obviousness of divine existence is due to a proper education or a social context in which divine matters are made salient. It also, however, makes a mistake with regard to immediate principles, by failing to recognize the limitations of the human mind. It may entirely be conceded that divine existence would be self-evident to God; but our minds are not able to conceive divine matters so fully and perfectly that we can assume this to be true of us. Thus someone may not understand the terms of the proposition properly. We see even with immediate principles that are directly within our reach, like the principle of noncontradiction, that people sometimes are confused about the terms; but we do not have the knowledge of what God is that would be required.
(1.2) With regard to the second, which holds that something divine is known directly by the intellect. This itself is of two kinds: one taking God to be primary object and one taking God to be known as light for other things known.
(1.2.1) We might hold that something divine is known directly by the intellect in the sense that God is the primary object of the intellect, as being the most fundamental thing about which we can think. But there is reason to think this false, because what the mind first knows must be most certain, but this is not so when we are speaking of God. It seems that we would therefore be required to say that God is in some way the object of our mind but not precisely known as such, which would appear to suggest that God's existence, as such, would then have to be known by reason, not immediate understanding. God far exceeds any object our mind can have, however. Therefore we read in Scripture (Ex. 33:20): Man shall not see me and live.
(1.2.2) We might also hold that something divine is known directly by the intellect in the sense that God is the light by which all things are known. Thus just as in visible things, we can see the light by which other things are made manifest, so in intelligible things, we can see the divine light by which other things are understood. However, this seems to elide different ways in which something can be responsible for knowledge. As Aquinas says (SCG 1.11.6), God is that by which all things are known, not in the sense that they are only known if He is known, as is the case among principles known per se, but because all our knowing is caused in us through His influence.
All of these positions ((1.1), (1.2.1), (1.2.2)) involve confusions about the mind and its objects. The position in (1.1) confuses the thing itself and the thing as it is an object of the mind; that in (1.2.1) falsely assumes that what can be an object of our mind must be a direct and immediate object; and that in (1.2.2) confuses something's being a cause or source of our knowledge with its being an object of our knowledge. The confusion is perhaps strengthened by the fact that each of these has a similarity to a truth, as we will see: with respect to (1.1), it is true that God's essence is His actual being and that God is first and fundamental with respect to all else; with respect to (1.2.1), it is true that God is first intelligible being, and that our intellect in some way has an orientation to Him; and with respect to (1.2.2), it is true that God is first light and the source of all understanding. But if we do not make the errors noted, we see that none of these things imply that God's existence is known by us through itself, immediately, or self-evidently.
(2) The second position by means of which one might oppose the claim that the existence of the divine is demonstrable is the opposite of the first. Some people, regarding the arguments given for the existence of divine things to be weak (whether, as in some cases, because they were really weak, or, as in other cases, because they had a faulty understanding of the arguments, or, as in yet other cases, because they had a faulty understanding of what was required and not required in order to prove that something exists), have come to the conclusion that the existence of God is not demonstrable at all but only credible; that is, that it is not known but is instead to be accepted wholly with the trust of faith. Thus while the first position held that divine existence is not demonstrable because it is known through itself and not through another, this position holds that divine existence does not admit of demonstration because we cannot know it at all, even in principle, and can only believe it to be true. As with the previous position, this would not rule out all argument for God's actually being; but these would, instead of establishing that conclusion as known, merely confirm its status as believable.
This position has a similarity to a truth we will discuss below, that some kinds of demonstration are impossible in this context, but it errs greatly through a failure to consider the diversity of the ways in which things are demonstrated. As God has effects, including sensible effects, and as we are related to God in certain ways, demonstration from those effects or relations are in principle possible, and therefore at least a basic demonstration quia is in principle possible, because we may argue from the effect to the cause.
From the failure of these two positions ((1), (2)), it is clear that whether or not there is something divine is something that at least in principle admits of demonstration, one way or another. We need, however, to know something about what kind of demonstration would be relevant in order to know whether it is within the scope of ordinary human abilities. For some things are perhaps demonstrable in principle but would require starting points to which we human beings do not have direct access.
Having considered whether the actual being of something divine could be demonstrated, we should then consider the way in which it would be demonstrated. From our reason for rejecting the position that God's existence could be known immediately, we can see that we can have no demonstration propter quid of the existence of something divine. That is, in order to have such a demonstration, we would need to know God's very nature, what sort of being a divine being is, as prior to His actual being. This is obviously not true; if God did not exist, we could not know His nature at all, and the human mind does not in any case have such a full apprehension of the divine nature as to be able to know what necessarily must follow from it. Nor is there anything prior to God in light of which He could be better understood. Thus we cannot have a demonstration propter quid that God exists, and for the same reasons we can have no demonstrative regress, because no amount of dialectical work will cross the insuperable gap between what God is in Himself and what our minds can understand.
Nonetheless, there are other forms of demonstration, and none of the things we have considered rule out a demonstration quia. We can know that God is without knowing what God's being is in itself, by knowing God from His effects. It is clear, of course, that we do reason from effects to causes in order to establish that things exist. Aquinas gives one simple and obvious example of how we do (In Symb. art. 1): Suppose someone at the entryway to a house were to feel heat coming from within, and, on proceeding deeper into the house, were to find that the heat increased. From this he would reasonably conclude that there was a fire in the house, even though he had not yet seen the fire. It is clear, moreover, that some such reasoning is demonstrative, namely insofar as definite effects require causes. As St. Thomas says (SCG 1.12.8), In arguments demonstrating that God is, it is not necessary to assume the divine essence or whatness (quidditas) as the middle term...but in place of the whatness, an effect is taken as the middle term, as is the case in demonstrations quia. And as he notes in the same place, our very names for the divine show this, since they are taken from effects attributed to God as cause. This is within our reach, because many of these effects are sensible effects, and thus if God causes sensible effects, we can know them, and if we can know them as effects, we can conclude to God as cause. Thus it is in principle possible to have a demonstration quia of the conclusion that there is something divine.
1.Pr.3 On Initial Indications that Something Divine Actually Is
We have seen that it is at least in principle possible that one could demonstrate that something divine actually is, that this could be done with an appropriate quia demonstration from effects, and that as the effects involved are sensible things, the starting points of such demonstrations could possibly be had. One might still reject the demonstrability of the position that divine things actually are by claiming that the contrary is already demonstrated. That is, you could hold that it is impossible to prove that anything divine exists on the ground that you have a proof that nothing divine exists. This is relatively uncommon, for those who think atheism demonstrable are relatively few in the world. This will be dealt with as we continue, for nothing is better for establishing the demonstrability of a particular conclusion than actually demonstrating it and showing how arguments for the opposed conclusion are not demonstrative. However, before we do so, it is worth considering the question of dialectical proofs as well.
There are many things that initially suggest that something divine actually is. Recognizing these indications at least gives us a reason to inquire into divine matters further.
(1) First, there are many apparent direct and indirect experiences of what is taken to be divine, which are popularly called religious experiences. These are of many different kinds. There are very common experiences, like a general sense of powerful presence or special raptness or sense of illumination in religious contexts; others are less common but more common than is sometimes recognized, like vivid sense of the numinous or visions and locutions; others are relatively rare, such as experiences of union; yet others appear to be relatively unique, such as some of the experiences of the Hebrew prophets or St. John, St. Augustine and St. Monica during conversation sharing the same experience of the Selfsame in the Vision at Ostia, or St. Teresa's experience of the angel and the Spear. But these are only some examples of note; actual cases are legion, found throughout the world, among Christians, Jews, Muslims, Hindus, Sikhs, and others of all varieties.
We do not interpret experiences in isolation; it is a grave error to look at a single experience and attempt to assess it without any regard to other experiences. It is also a grave error to consider only experiences of a single type, as if real things were not experienceable in many different ways. Nor do we in any field of human life restrict ourselves entirely to what one experiences in one's own person; we all rely on the second-hand experience that we have by relying on others. Nor can we prejudge experience beforehand, since it is with experience that our reasoning begins; when we determine that someone is hallucinating or that they are experiencing a delusion, this is not because of some prior consideration of the objects, but due to other experiences and what can be known from them.
It is true, of course, that individuals can have delusions and hallucinations, that people have on occasion had intense emotional connections to fictional characters, and are capable of misinterpreting even things that they really experience. But these are all things that are considered with regard to every kind of experience, and it is why one needs to rely not merely on personal experience but testimony, as well, and to consider experience widely rather than narrowly, taking into account indirect experiential connections as well as direct ones. When we do this, it is obviously false to claim that there is no evidence of the divine when so many people in so many circumstances have had so many different experiences of something divine of some kind.
(2) Second, the general consensus of peoples (consensus gentium) seems to suggest that it is natural for human reason to conclude that there is something divine of some kind. As human beings are rational and therefore civilizational beings, our very inquiry is social, requiring assistance from others in remedying the flows in our inquiry. Therefore all human beings at some time or another appeal to the fact that something is generally accepted, either among the wise, i.e., among those in a special position to know, or among the many. The latter provides the benefit of abstracting from the possibility of flaws in one's inquiry that are peculiar to oneself. It does not on its own rule out some more shared flaw. However, if one considers not one group but many groups, not one multitude but a multitude of multitudes, we may abstract from investigative flaws distinctive to particular groups, thus showing it to be reasonable to accept. As George Hayward Joyce says of a consensus gentium argument (The Principles of Natural Theology, chapter 5), "It rests simply on the principle that man's intellect is fundamentally trustworthy: that, though frequently misled in this or that particular case through accidental causes, yet the instrument itself is sound: that, of its own nature, it leads, not to error, but to truth."
Thus, for instance, assuming that other minds exist, we can recognize that there is a consensus gentium for the existence of a physical world that is independent of our minds; that is to say, there is a unity of custom among different peoples, despite radical differences in custom, environment, education, and the like, that is resilient over time in the face of many changes, establishing it to be reasonable. This will be true regardless of whether there are cases of individuals, out of their own peculiarities, freakishly insisting otherwise; and if anyone were to attempt to claim that there was no evidence for the existence of such a world, they would be adequately answered by pointing to the multitude of multitudes. Consensus gentium, therefore, is general evidence of there being particular evidence that can reasonably be interpreted as requiring the conclusion. Likewise, given the many variations in views about the physical world and its relation to the mind, it can only conclude to a general conclusion; the point it establishes does not close the inquiry but serve as a reasonable beginning in light of which one may inquire into more specific questions.
Consensus gentium arguments thus primarily differ according to the kind of reasonableness in view. Thus some are arguments from the authority of shared human reason; others are arguments to rational convergence as a mark or sign of truth; others are arguments to what is natural to reason to conclude.
In Cicero's De natura deorum, the Epicurean Velleius gives a consensus gentium argument for the existence of gods, saying (1.16), "For what nation or race of men is there, that does not possess, independently of instruction, a certain preconception of them?" He attributes calls this a prolepsis or preconception, i.e., "a certain idea of a thing formed by the mind beforehand, without which nothing can be understood, or investigated, or discussed." That is to say, even in order to investigate or discuss whether or not there are gods, one must also know what it is whose existence you are investigating or discussing. But, he continues (1.17), since we have an idea of them implanted in us, "and as that upon which the nature of all men is agreed must be true, their existence must be acknowledged." Cotta, the Skeptic, however, responds by saying (1.23) that there may be nations so barbarous as not to believe in the gods. Later, the Stoic Balbus argues (2.2) that the belief has remarkable stability and has been strengthened by the passing of time, which destroys mere imaginations and confirms judgments, and notes the position of Cleanthes that the idea of gods comes from four sources, premonitions of the future, benefits received from the world, terrors of unusual events, and the uniformity of the heavens. It is clear, then, that Balbus's argument is not, like that of Velleius, based on the notion of an innate idea of the gods; rather, the point is that human beings rationally converge on it over time; and, in particular, of course, he holds that they do so on the Stoic view of the divinely rational universe, although he holds that human beings also often fracture and confuse this by excessive indulgence of the imagination. Cotta will then argue that Balbus's philosophical conception of divinity is not better than the traditional conceptions, based in imagination, of non-philosophers. It is implied, and we learn from other works (Tusculan Disputation 1.13), that Cicero himself thinks there is something to the argument.
It can be seen then, from the deliberately constructed ambiguities of the argument in Cicero's account that assessing the force of the argument depends on one's account for how it is this that belief in divinity is so extensive and stable. In some cases, people posit that there is an innate idea or sentiment of the divine. In others, appeal is made not to innate idea but to innate yearnings or natural desires that are satisfiable only if there is something divine. In others, appeal is rather made to reason as commonly tending in the same direction. The more universal the belief, the better for the argument, and some people putting it forward do, in fact, put it forward on the assumption that universality can simply be assumed. However, strictly speaking, and contrary to many critics, no version of the argument requires strict universality rather than practical universality, just as no account of a normal course of development requires that there be no freaks of nature; the argument is a response to the people claiming that there is nothing divine, and thus is arguing at a level of abstraction from peculiarities of individual cases. As Charles Hodge notes (Systematic Theology, Volume I), "Should a tribe of idiots be discovered, it would not prove that reason is not an attribute of our nature. If any community should come to light in which infanticide was universal, it would not prove that parental love was not one of the instincts of humanity." And Turretin says (Inst. 1.1.16), "No more than the monsters and prodigies which are sometimes seen contrary to nature can overturn the regular laws established by God; or the instances of insanity overturn the definition of man as a rational animal." And this is indeed to the point, since in which people often accept consensus gentium arguments, such as the consensus gentium argument for basic moral principles, for the importance of art, for human fellow-feeling, it would not be to the point to indicate the existence of psychopaths, philistines, or misanthropes, although it can be reasonable to ask the question about the ways in which the common norm can degenerate in particular cases; these things are recognized as outliers. Critics are also too quick in their attempts to claim particular counterexamples; it is a common experience in arguing with atheists, even if not a universal one, to find the atheist believing in something, like truth or moral order, that other people would call divine in some way, and doing so in terms similar to the reasons why other people call it divine, but simply not thinking or even refusing to call it 'divine' for some personal or cultural reason. Questions of universality and counterexamples to it should not be handled glibly even in examining very basic and simple versions of the argument. However, it is also clear that versions of the argument based on reason are more tolerant of variation than those based on innate ideas or sense, and also more directly connect the matter with reason and truth rather than by way of ease of belief.
John Stuart Mill discusses this line of argument critically in his essay, "Theism", which is arguably the best known attempt at actual refutation. He takes the argument itself usually to be used to argue for a sense or intuition of God, but argues that where we have definite evidence, the people who affirm the existence of God typically appeal to things like the design of the universe, not an internal intuition. While it is true that this is one line that might be taken, Mill's assumption that the argument involves an appeal to an intuitive perception is not universal, as I have noted. He dismisses the beliefs in divinity common among the uneducated or primitive tribes on the hypothesis that it is mere animism arising from generalization. While the latter dismissal is typical of Mill, mere hypothesis does not do away with the fact that these are rational people who are indeed able to think, even if, unlike Mill, they lack the second-hand evidence that education provides individuals about the nature of the world through the testimony of more intensive researchers and their collators. Being accustomed from their earliest days to certain ways of viewing the world, steeped in them, people often underestimate the extent to which all their knowledge is dependent on the apparent consensuses among the people they know, and likewise inclined to overestimate the extent to which their own views are based on first-hand evidence; in reality, the difference is almost wholly in the education. But both the relatively uneducated nor tribal religions are human, and therefore rational, and their reasoning cannot all be shoved onto a single track.
Despite the failure of Mill's criticisms, however, there are certain 'defeaters' for consensus gentium arguments that arise from its structure. For instance, the consent of peoples by its nature does not take into account new evidence not commonly available, so that something held widely by many may turn out wrong, despite the aptitude of reason for truth, because while the conclusion drawn was reasonable on the evidence had, the new evidence may change the overall face of things. The second thing that might answer a consensus gentium argument, simply based on its structure, is evidence that the consensus is an imposed rather than a natural consensus; that is to say, that the consensus is primarily due to particular human beings exercising the power of reward and punishment against their fellow human beings in order to drive them in a particular direction. Against the first one might say that this consensus includes many who have familiarity with any new evidence that might be proposed, and against the second that the consensus is too wide to be artificial, but both of these arguments have been made, and if they were developed properly, which they rarely are, they would be more serious objections than anything Mill provides, and would have to be considered in any full development of the argument.
(3) Third, the existence of something divine seems suggested by certain prima facie features of the moral life. William Whewell gives an example ("The Moral Argument for the Being of God"), which identifies four major strands:
(a) Sentiment of dependence: "The consciousness of existence, when reflected upon, is calculated to fill the mind with a sense of mysterious awe." We feel our dependency, and thus look for some adequate being on which we are dependent.
(b) Sentiment of gratitude: "To be grateful for benefits is the instinctive prompting of our nature." We are, however, surrounded by many benefits, like those of nature, that are not owed to our fellow human beings. "Existence, with innumerable capacities and sources of good, is and must be felt by us to be a gift." Thus we often feel gratitude for these things. This inclines us to look for some being to which we can reasonably be grateful for these benefits.
(c) Sentiment of obligation: We have a moral constitution. "Among the necessary convictions of reason is the distinction between right and wrong, and the idea of duty or the moral law." We thus feel ourselves as under judgment and law in the tribunal of conscience and reason, and this leads us to look for "an Invisible Judge, who is the substance and administrator of the Moral Law". Further: "The ideas of right and wrong, merit and demerit, happiness and misery, are respectively linked each to each in the necessary convictions of the human mind." We recognize that virtue ought to go with happiness and guilt with misery. We do not find a world obviously like that, but this cannot change how we feel about it, because the feeling is rooted in moral reason. Thus we look for a being who can reconcile these things. We see this most clearly in cases where someone has a choice between life and duty, in which doing what is right will mean their death. If someone thinks that there is something that guarantees that death is not the whole story, that duty and happiness are ultimately united, however, then in that situation duty would be clearly more important than life. Thus "our practical principles -- the necessary dictations of our moral nature, impel us to act as though there were a God."
(d) Aspirational longings: "Ever stirring in the depths of the soul is the desire for Well-being, for Truth, Beauty, and Goodness -- the aspiration after something more blessed, true, beautiful, and good than can be realized here below." This aspiration cannot be satisfied with the finite; it includes a desire for what goes beyond death. "Admit the being of a God who implanted these infinite desires in the human heart, and then we may find a ground of hope. Admit the being of a God, and then we can reasonably account for it that we have desires so far transcending all this life can give; and we may hope that the longings he has himself inspired may by him be fulfilled."
Each of these is not really a single sentiment but a family of common sentiments; each family sets us to look for something real to correspond to them; each suggests the possibility that we might have these feelings for a reason. When we posit such a being ('superinduction' is Whewell's term for such positing), however, they in a sense jump together, by a sort of consilience, admitting of a unified explanation; Whewell takes this kind of consilience as a mark of intellectual progress. The identification of the sense of dependence is inspired by Schleiermacher, and the identification of both the sense of gratitude and the sense of obligation are inspired by Kant, while the identification of the aspirational longing a way of capturing aspects of our moral life that are of special concern to Platonists.
We have seen three lines of argument, experience both direct and testimonial, consensus gentium, and moral life, all three of which are historically quite influential. There is good reason to think that none of them are demonstrative, and, indeed, they are not usually put forward as demonstrative. The argument from experience is inductive rather than deductive, rising from particulars to universals. The consensus gentium is by its nature an indirect argument, and is generally recognized as such by those who take it to be important. Thus Flint says (Theism, Note VIII), "It is an evidence that there are direct evidences -- and when kept in this its proper place it has no inconsiderable value -- but it cannot be urged as a direct and independent argument", while Cardinal Mercier says (A Manual of Modern Scholastic Philosophy, Vol. II, section 32), "Its real value is that it supplies a presumption that valid proofs do exist." It also heavily relies on what is accepted by many, which is a sign of a dialectical argument from probable premises. Of the moral argument, Whewell says ("The Moral Argument") it is "a complement to the other arguments" and "one interesting portion of that various evidence which accumulates from every quarter around this great and central truth." It is, of course, not impossible that they could be transformed into demonstrations with further dialectical work to rule out alternatives and trace things back to immediate principles, tightening the arguments; but these three in particular were picked because they are arguments that admit of reasonable defense, but by their structure would require considerable work to make demonstrative.
Dialectical arguments can give very different kinds of results, and this is true here; one can draw different conclusions from the multitude of experiences, the consensus gentium, or the fit with moral life. Depending on how it is used, each of these indications, individually or in concert with the others, can be taken as (a) a heuristic, (b) a basis for a postulate for practical life or inquiry, or (c) a reason. Taken as heuristic, they allow us to consider various hypotheses that can then be further tested and refined; taken as grounds for a postulate, they allow us to assume their conclusion for practical life or further inquiry, until we have reason to change it; and as reasons, they provide support for suspicion, opinion, or belief.
But, suggestive as these might be, and even if we take them, individually or together, as dialectical proofs, in none of these things so far do we properly have a demonstration of divine things; we must look elsewhere for reason to think that the existence of divine things can be more than a convenient postulate, a reasonable suspicion, or a probable conclusion. In all fields of thought we should take with thanks any good reasoning we can get; but we should seek especially for demonstration when it can be had.
* See William A. Wallace, The Modeling of Nature, The Catholic University of America Press (Washington, DC: 1996), pp. 300-308, for a summary of Zabarella's conception of demonstrative regress and Galileo's adaptation of it.