I have done some very serious drawing in my sketchbook, by serious I’m not implying that the drawing was successful. Only that it was a serious attempt at interpreting what my eyes see or an attempt at resolving a drawing problem- proportion, perspective, values, etc. Or I just might be carried away with the moment and bring the sketch to a degree of finish one might associate with a finished piece and it just might wind up in a frame. A sketch can be thinking, doodling or just pushing paint, pencil or ink in one direction or another. Just having fun till some inspiration hits me. It could be the discipline of just wanting to draw or paint daily till that inspiration hits me and it spring boards into some larger work.
An artist sketchbook gives one the freedom to do all these things with no pressure other than honest effort and the enjoyment of doing the thing.
So what makes a sketch a sketch and separates it from what is considered a serious attempt at creating art. I don’t know, maybe it should be the other way around and one should bring that same mix of seriousness, play and enjoyment to a finished piece.