I had a teacher in art school named Rob Moore. He was an amazing teacher, a great teacher, but he didn't teach us anything. The only he ever told us was, "I'm going to use the word "form" to refer to three dimensional things, and "shape" for two dimensional things."
Rob was a really nice guy, but also a bit intimidating. We'd all actually signed up for life drawing, but Rob made a mistake and thought it was basic drawing. No one had the guts to correct him so, fortunately for us, we got basic drawing.
Rob started by sticking two gray squares of paper on the white wall. One was lighter than the other. He asked, "which of these is further away and which is closer?" One student answered, "the light one." "Really?", Rob asked, "what do you think?" he asked another student. "The dark one," was the answer. "Really?" asked Rob again. "Hmmm..." he said. A lot of classes went like that.
For the first assignment Rob told us to bring in a drawing the following week that we felt showed form in space. A few of us brought in these fairly elaborate, tight, pencil drawings - something which would have earned me big applause in the illustration department. All of the drawings went on the wall. Rob paced back and forth, and asked the class, "which of these drawings shows form and space?" Students pointed to this or that drawing, and Rob went, "really? hmm..." Then he stopped in front of a very simple (we thought, horrible, lame, stupid) drawing of the corner of a table that looked something like this:
He pointed to it and asked, "what about this one?"
For the next week Rob told us to get a pad of 100 sheets of paper, a green bell pepper and a Sharpie. We were to make drawings of the pepper (at least 100 of them), using a line that did not vary in thickness or color - just a uniform black line. He'd flip through hundreds and hundreds of drawings, dismissing most of them. Maybe he'd stop at one and say, "what do you think of this one?"
Sometimes I'd try to trick him by bringing in a variety of drawings, each using a very different approach. I'd get to class before everyone else, and stick them on the wall, spread out. By the time the other students put their work up you couldn't tell mine went together. Rob would point at one of my drawings and say something like, "maybe this person thinks a cast shadow says something about the form that cast it - who made this drawing?" I'd have to respond. He did the same thing with another, very different drawing. "You made both of these?", he asked. Then he'd just smile. He knew I was trying, even though my work was always used as the example of what didn't work.
Then one time I met with Rob to discuss where I was going with my painting. He looked at one of my early acrylic illustrations and said, "well, you're obviously enormously talented." wha... huh... As if things weren't already confusing enough. I couldn't tell if I was being insulted or what.
Rob gave me doubt. Doubt is a really, really good thing. I was determined to find out what was going on, what I wasn't able to see, no matter how long it took. It took a decade or two, and now at least I can see what Rob was seeing, in some measure. Now I don't believe anything except my own eyes.
I dug out my class notes - stuff I'd written down with exclamation points and question marks, little drawings I'd made of the other students' work and what Rob was saying (or not saying, but implying) about it. It was like finding some ancient text and finally being able to translate it.
We lost Rob midway through classes in December 1992. Over the years I've flip-flopped in my opinion of his teaching methods. As I have figured some things out, learned to see them myself, I've sometimes thought, "couldn't he at least have told us that?" Maybe. But when we're told things really explicitly we may think, "ok, I know this subject now" and that's that. When a good teacher - I'll call him a master - is able to simply point you in the right direction then you just keep going. You never reach the end, because there isn't one.