The Problem with Impure Infinitism

It is generally believed that pure versions of infinitism face two problems, namely: 1) they are unable to distinguish between potential and actual series of justified reasons because they are defined strictly in terms of relations between beliefs in the series so that every succeeding belief is justified by the belief before it and so on ad infinitum and, 2) they are unable to mark the difference between a set of justified reasons that are connected to truth and one that is not because they are defined strictly in terms of a relation between beliefs in the series of reasons. However, Aikin argues that impure infinitism could surmount these problems without undermining the infinite regress condition because impure infinitism can solve the Modus Ponens Reductio, MPR, argument that threatens pure versions of infinitism. I argue that Aikin does not succeed because his impure infinitism faces some fatal consequences and any attempt to salvage it will undermine the infinite regress of justification.