Form, in the narrow sense, is nothing but the separating line
between surfaces of colour. That is its outer meaning. But it has
also an inner meaning, of varying intensity, [Footnote: It is
never literally true that any form is meaningless and "says
nothing." Every form in the world says something. But its message
often fails to reach us, and even if it does, full understanding
is often withheld from us.] and, properly speaking, FORM IS THE
OUTWARD EXPRESSION OF THIS INNER MEANING. To use once more the
metaphor of the piano--the artist is the hand which, by playing
on this or that key (i.e., form), affects the human soul in this
or that way. SO IT IS EVIDENT THAT FORM-HARMONY MUST REST ONLY ON
A CORRESPONDING VIBRATION OF THE HUMAN SOUL; AND THIS IS A SECOND
GUIDING PRINCIPLE OF THE INNER NEED.

The two aspects of form just mentioned define its two aims. The
task of limiting surfaces (the outer aspect) is well performed if
the inner meaning is fully expressed.

[Footnote: The phrase "full expression" must be clearly
understood. Form often is most expressive when least coherent. It
is often most expressive when outwardly most imperfect, perhaps
only a stroke, a mere hint of outer meaning.]

The outer task may assume many different shapes; but it will
never fail in one of two purposes: (1) Either form aims at so
limiting surfaces as to fashion of them some material object; (2)
Or form remains abstract, describing only a non-material,
spiritual entity. Such non-material entities, with life and value
as such, are a circle, a triangle, a rhombus, a trapeze, etc.,