I can say without a doubt, that getting high before a philosophy class, is a bad idea. Your teacher is not retarded, he/she knows you are high, and worse yet you will say some pretty damn retarded stuff that seems brilliant in your own head.

High philosophy is great when you are talking about just talking philosophy amoungst friends, but there is a stark difference between a philosophical discussion, and taking exams on philosophical principles/people/events/etc.

I didnt start smoking until the second half of my freshman year in college, and as a philosophy major, and my philosophy teacher flat out came up to me and had a talk because she noticed the difference. Thats not to say everyone will be the same as me...

But I was a solid B student, who could have gotten an A but just didnt care enough. I was one of the most vocal students in my classes, and regularly had after class chats with my teacher, just about whatever she had talked about that day. The fact that she noticed the difference in my thought process, and my participation, said alot to me back then, and was enough for me to stop smoking before class, because at the time I, like you, thought it would be a great idea and only help.

Most philosophy tests, outside of graduate level courses, are going to be essay and multiple choice kinds of things, based on the things you have learned during your time in class. Which means you need to either have really learned what was being taught in class, or have a damn good ability to memorize facts... pot doesnt really help much with the memorizing, although I suppose it would allow you the ability to get more into the class learning wise if it caught your interest.

As always, YMMV, and you will never really know unless you try, but from personal experience in the exact situation you are talking about, I wouldnt recommend it. Get high after class, get high any other time, but I just dont see it as a good idea to be high during class.