  The importance of some sort of causal link between the original producer of the name and the individual named and its relation to the representative nature of even singular concepts was brought out by Buridan and Dorp in their discussion of two cases. In the first case, Plato and Socrates are exactly similar and, without my knowing it, one replaces the other in my field of sight. Buridan and Dorp argue that while my first-formed singular concept is equally similar to the second person to appear, it is not a concept of him, because it is caused by a different individual. The criterion for distinction is not the fit between concept and object but the causal relation.  The second case was discussed by Dorp alone.  If identical twins are born, and are both called ‘Socrates’, it may seem that ‘Socrates’ will function as a common name in this case, because the concepts will be exactly alike, but here too the causal relation becomes all-important.  There are two singular terms, each with its own signification.