I believe that concept and plot are related by observation of realistic drawing rules (ie. perspective, depth cues and foreshortening); emotion and character by expressive line (and/or colour) (ie. emanatae, abstract visual elements).
In the little treatise-cum- instruction supplement to the last issue of Comic Art, Cartooning: Philosophy and Practice, Ivan Brunetti says that the minimum job of cartooning is to convey the visual characteristics necessary for us to recognise drawings as symbols.
Brunetti illustrates - see what I did there? - with an exercise in which one draws several everyday subjects (a car, a cat, a castle, yourself) a number of times, in successively shorter periods (2 minutes, 1 minute, 30 seconds, etc.), forcing one to strip down images to their essential elements.
As Brunetti says:
“...When we really have too little time to ‘think’ about the drawing we get closer to the ‘idea’ or essence of the thing being drawn. Here we begin to see the universal, latent, symbolic, visual, mnemonic language that is comics.”Brunetti argues that the goal of cartooning is to reach a compromise between the drawing that satisfies its fictional requirements to occupy space in the visual world of the comic and its function as a symbolic element of the story (ie. the drawing must ‘feel’ physically solid and be ‘readable’ as a symbol).
Jessica Abel and Matt Madden seem to agree. The first exercise they set in Drawing Words & Writing Pictures suggests that one tries drawing stick men. I think cartooning owes a lot more to the discipline of design than is commonly acknowledged and that, in many senses, comics stand or fall on this strength.
Is it necessary to be a good draughtsman to be a good cartoonist? No, it's not necessary, but to be a good cartoonist without being a good draughtsman requires exceptional storytelling. A reasonable storyteller with strong drawing skills is unlimited in terms of storytelling. Lots of amateur cartoonists fail because they want to tell stories beyond their drawing ability.
It’s perfectly valid to criticise comics on the basis of their art; perhaps it is the most valid basis for criticism. As Dez Skinn writes in the introduction to Comic Art Now, comics are and have always been about the artwork.