There is an interesting exercise that I think is valuable for every philosophy professor at some point in his or her career to try: try to pin down exactly what an 'Introduction to Philosophy' course is, using the different standards to which we actually hold such courses. What can easily be found when one does this is that Intro courses are in reality jumbles. If you were to take typical Department-mandated objectives for Intro courses and design a course specifically to meet those objectives, then another standard, like the typical prerequisite structure of a philosophy major, and design a course specifically to contribute in an optimal way to preparing for the courses for which it is a prerequisite, then another standard, like actually introducing people to philosophy, and design a course specifically with that in view -- if, I say, you were to do this through all the different standards to which Introduction to Philosophy courses are held, I think you would quickly find that none of the courses would obviously be the same course.
There are a number of different functions an 'Introduction to Philosophy' course could have. It could be the kind of course that used to be called Philosophical Encyclopedia, which was basically what the title says: it was a tour of philosophy, involving a very brief historical survey, a look at some of the major positions of some of the major philosophical disciplines, and, often, a guide to students as to what might be worth reading on their own. Nothing about the course particularly required that students do philosophy, beyond what was required to follow the basic ideas in very broad outline, but it wasn't intended to do so: it was intended, like a logic course, to give students basic tools (distinctions, classifications, general concepts required for historical comparison), and perhaps also to give them a sense of where they might head next. This is a perfectly reasonable thing to have a course for. There's a perfectly straightforward sense in which, done properly, it would be a solid and useful 'Introduction to Philosophy' course. Intro courses tend not to fulfill this function particularly well, but if you look at a lot of course objectives for them, it's pretty clear that they are, at least in principle, supposed to fulfill it.
Another possible approach might be to treat it as a course in philosophical writing. That there is often a need for something like such a course is usually quite obvious to those who have to grade student papers. Philosophical writing takes certain skills of analysis and organization, and it is really not fair to students to expect that they will already have them or will just pick them up on the fly or will somehow gain them through 'feedback' from the professor, particularly since assignments and feedback are often not particularly well designed for doing this. (I could write another post entirely about peculiarities and defects in how people seem to think of and handle feedback to students, and the difficult problems of doing 'feedback' in a way that could seriously be considered useful for students themselves.) But most Intro courses are not set up with a focus on writing.
A different kind of approach might be to focus on philosophy majors, making the Intro course a gateway to the major. It is quite clear that Intro courses are often treated as fulfilling this function. To fulfill this function properly, however, the course should set students up to succeed in future philosophy courses. This is arguably the function that Intro courses usually fulfill best, but I would argue that they often don't fulfill it very well, either, not so much from lack of trying as from the limits on our ability to anticipate what students would actually find useful in future courses. Philosophy is an immense field; in one way or another it covers everything. And if you start asking specific questions about how these courses set students up for success, you often find that there is no obvious answer to the question. If, for instance, the Intro course is supposed to set up for courses like Ancient Philosophy, Medieval Philosophy, and so forth, why don't more Intro courses have extensive discussion of actual Stoic and Neoplatonist figures and ideas? If it is supposed to prepare for courses more focused on analytic-style problems, Philosophy of Mind, for instance, why don't more Intro courses have a significant logic component? There are lots that don't.
Many philosophy professors really want their Intro courses to be introductions to doing philosophy. Ich habe nicht die Absicht die Philosophie zu lehren sondern philosophiren zu lehren. But if you look at course descriptions, course objectives, prerequisite structures, and the like, it's often less than clear how these fit with how teachers often go about trying to get their students to think through philosophical issues in philosophical ways.
The list, of course, could be extended indefinitely, using things like actual methods of evaluating teaching, or departmental policies, or even the practical fact that Intro courses tend to function as 'advertising' by which departments recruit philosophy majors in the first place. The real point here, of course, is that it's difficult for Intro to be a good introduction because there are so many conflicting ways to be an introduction, all of which are on the table and none of which are easy to exclude given all the standard pressures that go into designing and teaching an Intro course in the first place. If you go through all the course objectives, department policies, things that come up in the evaluation process that professors need to show that they do in order to have a proper evaluation portfolio, there is too much expectation put on the table. No matter what anyone does, something is going to be shortchanged. You can get some amusing confirmations of this if you get a bunch of philosophy professors together to talk about Intro courses; they rarely have the same idea of what an Introduction to Philosophy course should be and are often aghast at how other philosophy professors run their Intro courses, despite the fact that those others can virtually always justify their approaches by one of the jillion different standards on the table.
Ideally, I think, there would be an Intro course qua Philosophical Encyclopedia, and an Intro course qua Philosophical Writing, and an Intro course qua teacher and students trying to think through philosophical questions together, and so forth. There's no obvious reason why all of this should be stuffed into the same course; when you try to do it, it's easy for one to crowd out the others. The problem, of course, is how to make something like this practicable given common administrative expectations and the sheer inertia in how faculty tend to handle basic courses in the first place.
