I've had photographs taken for portraits because I very much prefer working from the photographs than from models... I couldn't attempt to do a portrait from photographs of somebody I didn't know.
I foresee it and yet I hardly ever carry it out as I foresee it. It transforms itself by the actual paint. I don't in fact know very often what the paint will do, and it does many things which are very much better than I could make it do.
It is rightly laid down that 'true knowledge is knowledge by causes'. Also the establishment of four causes is not bad: material, formal, efficient and final.