The figure of speech the simile and the metaphor both institute a comparison or show a similarity between two things or subjects different in kinds. But the comparison is not made in the same way in them. In the former, the likeness is clearly shown by the employment of the words like, as, like, etc. But in the metaphor, the resemblance between the things or subjects is kept implied.
A simile, thus, differs from a metaphor only in form, and not in content. What is distinctly expressed in the simile, is only implied in the metaphor. A metaphor is, in fact, a compressed simile, and, in the same way, a simile is an expanded metaphor. The best test of a metaphor is found in its expansion into a faultless simile and vice versa.
Thus, the example- ‘The eldest son is the star of the family’- can be expanded thus-‘Just as a star is bright, so the eldest son is the bright member of the family.’ This is the form of a simile. Similarly, the metaphor in the sentence, “He is the pillar of the state,” can be expanded into a simile thus: “Just as a pillar supports a building, so he supports the state.” Again, the simile in the expression-“Red as a rose is she”-can be compressed into the metaphor-“She is a red rose”. Again, in simile “His heart is as hard as a stone” can be expressed as “He has a stony heart” in metaphor. The simile “The camel crosses the desert, just as the ship crosses the sea” can be expanded into a metaphor thus: “The camel is the ship of the desert.”