The Art Spirit
I thought Robert Henri's The Art Spirit would be one of those feel-good books of little substance, but it's actually changed the way I think about art.
In it, Henri writes:
"It is useless to study technique in advance of having a motive. Instead of establishing a vast stock of technical tricks, it would be far wiser to develop creative power by constant search for means particular to a motive already in mind, by studying and developing just that technique which you feel the immediate need of, and which you alone will serve you for the idea or the emotion which has moved you to expression. You will not only develop your power to see the means, but you will acquire power to organize that means to a purpose."
I finally finished the book today, lying on the couch with a stomach ache while the boys played. It's one I'll definitely keep on the shelf to reference from time to time.