This question is also of great interest to me. I've thought in the past that it would be good if people could just take uni exams without having the do the course itself. A lot of the time I learn for my studies mostly by finding a textbook that I like, usually not the recommended one, and reading all the relevant chapters, so I've thought sometimes, why do I need to pay for lectures when I can pretty much understand it on my own?
I guess the trouble with that is that you wouldn't become familiarised with the institution and its way of thinking. It shouldn't be an issue, but it is. I've found when I don't attend many lectures, I find exams harder because I'm not so much on the lecturers wavelength.
In another department, I bought a bass guitar recently, and have been thinking about asking a bassist for help with how to hit/pluck the strings, but at the moment I'm leaning towards just experimenting with different approaches, what feels comfortable and sounds good. It's an area where different players vary a lot, so it might be an opportunity to develop my own style from the outset, rather than following a so-called 'correct way'. But I'll see how I get on with that one.
I think the effectiveness of self-education probably depends largely on how good your instincts for that particular area are. I've done plenty of music stuff before, and it comes quite naturally to me, so I have some confidence in attempting this. However, I wouldn't try and teach myself how to build a wall, because it would be foolhardy, and I would just waste time and resources in the likely event that I would get it wrong.
But then again, to what extent is my belief that I couldn't build a wall based on a societal attitude that such things can't be done without training? |