Line is like a path that leads the "eye" around, within and sometimes through  form. Outlines follow the outer edges of a form or shape like a silhouette. Outlines are flat. Contours on the other hand are volumetric or three dimensional. They identify interior volumes as well as outside edges. There are two extreme approaches to rendering line drawings: Gesture and Contour. Both exhibit a sense of touch or three dimensional volume. In addition, "accented" lines - lines that swell or move from thick to thin and light to dark- are more dimensional than lines that are the same thickness or value throughout. Look closely at the line "quality" of the drawings below.

Jeremiah Hatcher

Contour Drawing is a methodical and deliberate approach to rendering form.  It is generally slow, employing a single, incisive line. There are no tonal areas applied (i.e. shading). Contour drawings are strictly line. As mentioned above, contours identify interior as well as exterior volumes.

Jeremiah Hatcher (Line Gesture)

Gesture Drawing is a quick and spontaneous, all encompassing approach to rendering form.  Because the artist is moving quickly, he or she draws through forms as though they were transparent.  You draw all around the form- front, back, top, bottom and sides- as though you were wrapping the form in wire creating a cage or armature. The intent is to generalize forms, leaving out details and specifics. Due to the spontaneous and immediate nature of being "gestural", gesture drawings are more expressive than contour drawings.
In class, we address four approaches to gesture: 1. Line 2. Mass 3. Line and Mass combined 4. Scribble. The drawing above is an example of Line Gesture. Notice how it identifies the structure of the forms. Mass and Scribble Gestures capture the mass and volumes of forms while creating a sense of light at the same time. This is because the two techniques are tonal in method. (Even though the Scribble technique is linear, the grouping of lines reads like a tone. Lines closer together create dark areas, lines further apart create light areas).
Mass Gesture

Scribble Gesture