In reasoning by analogy, we project a queried property from one or more source cases to a target case on the basis of one or more assumed similarities. There are three ways in which such reasoning can be inferentially sound. First, the variables of which the assumed similarities are values may determine, tightly or loosely, the variable of which the queried property is a value. Second, we may recognize that the source cases have the queried property in virtue of having the assumed similarities. Thirdly, and most weakly, sources and target may share many and varied similarities and have few dissimilarities.