Aristotle Rhetoric 3.4

[1] 20 The simile also is a metaphor; for there is very little difference. When the poet says of Achilles, ¹ it is a simile; if he says, a lion, he rushed on, it is a metaphor; for because both are courageous, he transfers the sense and calls Achilles a lion.

[2] The simile is also useful in prose, but should be less frequently used, for there is something poetical about it. Similes must be used like metaphors, which only differ in the manner stated.

[3] The following are examples of similes. Androtion ² said of Idrieus that he was like curs just unchained; for as they attack and bite, so he when loosed from his bonds was dangerous. Again, Theodamas likened Archidamus to a Euxenus ignorant of geometry, by proportion; ³ for Euxenus will be Archidamus acquainted with geometry. Again, Plato in the Republic ⁴ compares those who strip the dead to curs, which bite stones, but do not touch those who throw them; he also says that the people is like a ship's captain who is vigorous, but rather deaf; ⁵ that poets' verses resemble those who are in the bloom of youth but lack beauty; ⁶ for neither the one after they have lost their bloom, nor the others after they have been broken up, ⁷ 1407a 1 appear the same as before. Pericles said that the Samians were like children who cry while they accept the scraps. ⁸ He also compared the Boeotians to holm-oaks; for just as these are beaten down by knocking against each other, ⁹ so are the Boeotians by their civil strife. Demosthenes compared the people to passengers who are seasick. ¹⁰ Democrates said that orators resembled nurses who gulp down the morsel and rub the babies' lips with the spittle. ¹¹ Antisthenes likened the skinny Cephisodotus to incense, for he also gives pleasure by wasting away. All such expressions may be used as similes or metaphors, so that all that are approved as metaphors will obviously also serve as similes which are metaphors without the details.

[4] But in all cases the metaphor from proportion should be reciprocal and applicable to either of the two things of the same genus; for instance, if the goblet is the shield of Dionysus, then the shield may properly be called the goblet of Ares. ¹²