  How one is to describe these cases is, in some respects, a matter of controversy. Some philosophers think one can talk of vague identity or partial identity. Others think that such expressions are nonsensical. There is no space to discuss this issue here. It is enough to assume, however, that questions of how one is allowed to use the concept of identity effect only the care with which one should characterize these cases, not any substantive matter of fact. There are cases of substantial overlap of constitution in which that fact is the only bedrock fact in the case: there is no further fact about whether they are ‘really’ the same object. If there were, then there would have to be a haecceitas or thisness belonging to and individuating each complex physical object, and this I am assuming to be implausible if not unintelligible. (More about the conditions under which haecceitas can make sense will be found below.)