 We call the principle “Mere Lemmas” because the idea behind it is that if a proposition is a mere lemma, in the sense that it derives all of its justification from some prior evidence e, then it doesn’t have justificatory powers of its own, independent of the justificatory powers of e. Suppose, for instance, that you start out by knowing that Jim has a pet, but you don’t know what kind of pet it is (the example is from Pryor 2004). Then you come to know that it is a hairless pet. Now you become justified (perhaps to a small degree) in believing that Jim’s pet is a hairless dog. That is to say, whatever degree of justification you had before to believe that Jim’s pet is a hairless dog, you are now somewhat more justified in believing that same proposition. That Jim’s pet is a hairless dog of course entails that Jim’s pet is a dog. But your justification for believing that Jim’s pet is a hairless dog cannot in any way be transmuted into justification for believing that Jim’s pet is a dog. Whatever degree of justification you had before for believing that Jim’s pet is a dog, you are now less justified in believing that same proposition (because hairless dogs are a small minority of hairless pets).