 The most significant problem facing Similarity 1 is that without constraints on what counts as similar, any two things can be considered similar (Aronson et al. 1995: 21; Goodman 1972: 443–444). This has the unfortunate consequence that anything represents anything else. A natural response to this difficulty is to delineate a set of relevant respects and degrees to which \(M\) and \(T\) have to be similar. This idea can be moulded into the following definition: