"It is very strange to suggest that being a hammer comes first and is then followed parasitically by the traits that enable the entity to function as a hammer. I should like to know where in Heidegger's account anything of this sort is said or even suggested. The account given by Nikhil seems even to require that "hammer-hood" be an innate concept: in order to use anything as a hammer it must "always already" be understood to be a hammer. How would the use of hammers ever have come to be instituted?"

The thing that follows parasitically is the hammer's presence-at-hand. (This is obviously a term of art for Heidegger and I'm not sure if it can be analyzed as "traits that enable the entity to function as a hammer.") Maybe we can say something like the "objecthood" of the hammer is what is parasitic. In that case I am saying that it is first a hammer and then an object. It only becomes an "object" rather than a hammer in some degenerate cases (like when it breaks).