 With these provisos, and barring for the moment the complications arising from the consideration of intensional factors (such as time and modalities), we may proceed to review some core mereological notions and principles. Ideally, we may distinguish here between (a) those principles that are simply meant to fix the intended meaning of the relational predicate ‘part’, and (b) a variety of additional, more substantive principles that go beyond the obvious and aim at greater sophistication and descriptive power. Exactly where the boundary between (a) and (b) should be drawn, however, or even whether a boundary of this sort can be drawn at all, is by itself a matter of controversy. 