An analogy compares two subjects to focus on the similarities
An analogy often takes the form of the following: eye is to see as ear is to what? (Often denoted eye:see::ear:?) The answer is, of course, hear. One compares eye with ear, establishes the differences, then applies the difference to the word see, to find its counterpart. So, as the function of an eye is to see, the function of an ear is to hear.