LINE Line is a surprisingly difficult concept to define. My dictionary gives 86 definitions for line. The simplest explanation is that it is a long thin shape that ceases to act like a shape and acts like a . . . . . line. Lines are basic to all of the visual arts. Drawing is more or less based on using lines. Lines have many uses in pure design as well. The odd thing about lines is that they do not occur in nature. There are cracks and edges, long thin strands etc. But
those things either have mass (are objects) or are edges of objects. Line in art is an artificial device that we have learned to interpret as representing something. You have learned to read drawings with lines since childhood. The usual meaning of a line is that it represents an edge.
The Swiss artist Paul Klee defined line as a dot out for a walk.
CONTOUR .A contour is a line that defines or bounds anything -- defines its edge. Most lines in art are contour lines. An object does not have a line around its edge, nor anything that looks like a line. Yet when you see a line drawing you have no trouble interpreting the image as representing something in the real world. There are more contours on any complex object than the outside edge. There are many more subtle contours that can be seen and drawn. Things like folds and color changes can be represented by contour lines -- anything that has an edge.
Blind contour drawing is when you imagine that you are a machine that records exactly what your eyes see. You do this without looking at your drawing (blind) to keep the nosy left brain from criticizing your work. You record with your pen(cil) exactly what your eyes see as they slowly trace the edges of your subject. You must draw very slowly to further frustrate your impatient left brain into submission.
Modified contour drawing is one step removed from blind contour drawing. Here you only draw when you are looking at the subject but may look at your drawing occasionally.
When you look at your drawing, to see that you are in the right place and to check your progress, you must not draw.This makes sense because when you draw while looking at your drawing you are either drawing from memory or making up what you draw. The information you need to record in order to draw realistically is only available when you look carefully at your subject.