One and the Same

The expression “one and the same” must be used carefully in order to avoid blurring the distinction between numerical and qualitative identity. Although two things may be qualitatively identical (identical in the sense of sharing all the same qualities), they cannot be numerically identical (identical in the sense of being the same thing) unless they are in fact only one thing and not two separate things. To say that two things are one and the same is therefore to say not only that there is no difference between them, but also that they are in fact only one thing and not two separate things. Thus, for example, Los Angeles and the largest city in California are one and the same, because the name “Los Angeles" and the description “the largest city in California” refer to the same thing (the name and the description have qualitatively and numerically identical referents). For two things to be one and the same, they must be devoid of not only any qualitative, but also any numerical difference or distinction.