Discussion: Convex lines and the figure

I have run across the idea that the human form should be drawn only with convex lines because "there are no concave lines in the figure." The argument goes that the outer contours are governed by the bulging masses of the bones and muscles. Even when you cup your hand, your hollow palm is made up of a set of smaller convex shapes. Convexity is synonymous with life, volume, and fullness. Even on a thin person, the planes and lines should gently curve outward. Concave contours can be conceived as a series of overlapping convex forms.

The opposing view is that the figure is made up of a variety of lines and planes, including straight and concave. Some artists emphasize only straight lines, especially in the layin. Regarding concave contours, elastic skin stretched across any acute angle will form a concave shape, such as on the inside of the elbow or the curve of the neck. This would be true even on Mr. Universe or a heavyset person. Concavity is expressive of receptivity and inertness. Variety is the spice of life, and good drawing is a product of contrast.

I haven't made up my mind yet on this issue, and would be interested in your comments. Maybe you can make one case or the other better than I can. What have you been taught, and what thought process produces the best for you? You can also add your vote to the poll at left.