 In this section, we are interested in the possibility of the type of strong metaphysical infinitism that denies all of the three requirements. The denial of  (MF)  entails that there are at least some entities that are non-fundamental yet do not depend for their being on any fundamental entity or entities. There may be several ways in which this could happen, but the most extreme possibility is a type of infinite complexity whereby there is an infinite descent of different kinds of entities, each depending on entities further down the chain but never terminating and never being “fully accounted for”. We might think of this in terms of a violation of the principle of sufficient reason (PSR), at least if (PSR) is thought to require that we must reach an ultimate reason rather than just a reason at each layer below the previous one. Accordingly, infinite complexity entails a lack of structure with the type of explanatory import that (PSR) requires. This type of view would be more radical than the various, potentially innocuous types of infinite descent outlined so far. The view might strike many as implausible, at least when it comes to the actual  world.[25]