The principles of design are the fundamental parts of an artwork. Identifying these principals is one way to understand an artwork.
Form is an element of design closely related to shape, but form is always three demensional. A form is measurable by length, width, and height, and encloses volume. Forms can be actual 3-D forms created with sculpture or architecture, or they can be implied forms where the artist creates the illusion of the form onto a flat surface.
While a two-demensional shape can be seen from only one side, a three-demensional shape can be viewed from any side.