The relation between literal and transferred meanings is sometimes similarity and sometimes another connection. Fine speech described as pearls belongs to the first kind.
A whole word may also refer to a part, for example when “fingers” refers to fingertips inserted in the ears. This relation is whole-to-part, not resemblance in beauty or form.
Thus, isti'ara (metaphor) rests on similarity; majaz mursal rests on a different relation. The latter receives its own detailed treatment in the following level.