Sorry about the lack of posts recently; I have something like a jillion posts that have been 'in the works' for several weeks now, but things keep coming up and, frankly, nothing's really going to move to final stages until I've actually had a few days to recuperate from what was a very brutal end of term. However, this one is pretty much ready to go. While my intro course is necessarily limited, for a number of reasons, in how much time can be spent on Aquinas, I usually spend a class on him, and there's usually a question on one of the take-home quizzes asking students what they think the weakest premise (defined as the premise that would be hardest to defend, whether it's actually true or false) of Aquinas's First Way is. The primary point of the question is for students to show (1) that they know what is meant by "Aquinas's First Way"; and (2) have at least a very basic idea of how it works. But I've been collecting the basic answers given in order to get a better sense of what people's first impressions of the argument are, and twice posted them here (I, II), both because it's convenient having them here and because some of my readers would certainly be interested. So here we go again. This group was more inclined to answer the question in some detail; I usually get a few brief sentences, but most of the students went on a bit longer this time, for reasons I don't know.
The usual caveats apply. The following are not word-for-word the answers given, which are not needed for what I am doing here; I have simplified and paraphrased them, sticking as closely as possible to the meaning. This is not for the purpose of mocking my students; most of them have barely heard of Aquinas, if at all, when they come into my class, and they are trying to answer the question on the basis of a single class's discussion, not all of which was devoted to the First Way in particular, and, what is more, I don't think it's fair to demand that people pick up immediately ideas and concepts Aquinas himself thought could only be properly understood at the end of long, hard analysis. But even answers that show confusion can show that students are asking the right questions, and I think one sees that here. I have also ignored the answers that were just mere fluff.
You'll note, incidentally, that there are a few cases where people identify as the 'weak premise' what is actually the conclusion; I think these in fact should usually be read charitably as just the claim that they don't understand how the premises yield that conclusion in particular -- i.e., they are puzzled as to why someone would think that that conclusion follows from everything else, or else they don't understand what the conclusion is supposed to mean, even given the premises, or else they have the idea that to get that type of conclusion you'd have to use a very different kind of argument. And this can be a legitimate puzzle, and is I think a common type of reaction to arguments like the First Way even among intelligent people; so I've kept them, even though they aren't talking about a premise.
* That the thing which is moved cannot be moved by itself. Or what is moved must be moved by another. It is hard to say definitively that there is nothing that moves itself except for the one unmoved mover. Also to argue this would mean that we have no freewill because if only the one unmoved mover could move itself then that would mean that we don't move ourselves but our every choice is purely a product of other movers. Unless the unmoved mover moved our freewill into motion and perhaps also keeps it sustained.
* That there is an unmoved mover. It would be difficult to understand how everything that has moved has been moved by something else but yet there is one thing that has moved but not by anything else. You would have to give an example, such as that of how a trap works, to explain how the unmoved mover set the trap in motion. But someone might then argue that he couldn't be unmoved and also set the trap in motion.
* "Nothing can be at once in both actuality and potentiality in the same respect (if both actual and potential, it is actual in one respect and potential in another.)" You would have to prove what actual and potential motions are possible for it.
* "This first mover everyone understands to be God." Not everyone believes in God. Therefore this would be a hard premise to prove.
* "For motion is nothing else than the reduction of something from potentiality to actuality." It would be very difficult to prove that movement is a reduction from potential to actual, meaning from a state of nothing to a state of something by a negative median.
* The infinite regress premise, because it has to go all the way to the beginning and to find something that is the original mover, the main cause, has not been moved, and is God.
* Nothing can move itself. He didn't strongly defend it. He didn't look at other things like nature. Some things just change and move as time passes.
* I don't see how if something goes on for infinity there would be no first mover. It seems to me you need a first mover in order to have the possibility of infinity because that's what starts the action.
* That of the series not continuing infinitely and there being an unmoved mover. It would be hard to prove that this isn't really infinite.
* "If, then, that by which something is moved is moved, then it, too, must be moved by another, and that other by still another. But this does not go to infinity." This is subjective in that if an object is moved by another, and that other is moved by something else and so forth then who's to say that these objects don't keep getting moved one after the other. The part when it says that this does not go on to infinity is the part of the premise that threw me off. An object could keep on being moved forever.
* The necessity of the unmoved mover. The idea is that something in motion puts something else in motion, and this can be traced backwards. Since this cannot go back towards infinity (if there is no start, how can anything ever have been put into motion to begin with), the idea of the unmoved mover is put forward as a starting point. But to do this one must have excluded all other causes of motion, such as natural laws.