Are metaphors elliptical similes?

What is the relation between metaphors and similes? Aristotle's "comparison theory" holds that metaphors are elliptical similes: "Sam is a pig" is simply a short form of "Sam is like a pig." In contrast, it has been suggested that metaphors cannot be elliptical similes because metaphors are "stronger" than similes. We know metaphors are stronger, it is argued, because of examples involving corrections, such as "Peter is not just like a rock, he is a rock." The argument from corrections can be challenged on logical and empirical grounds. The ability to correct a simile with a metaphor does not entail that metaphors are stronger than similes when used on their own, which is likely to be the most frequent case. Although four experiments indicate that when corrections are involved, metaphors are indeed stronger than similes in several respects, alas a further four experiments indicate that these differences are largely eliminated when metaphors and similes are used on their own. We note that this pattern of results is consistent with the comparison theory, and we offer an explanation of the effects of corrections.