I outline a version of idealism that borrows from Humean Supervenience. The resulting theory is immune to what is often considered to be the most powerful anti-idealist argument, the gist of which is that the idealist can’t supply truthmakers (or an adequate supervenience base) for commonly accepted truths about the physical world. That charge has no purchase on Humean idealism.

This paper addresses what I call ‘the constitutive question’ concerning the rules we follow: namely, what determines the standard for a rule's correct application. John McDowell has offered a putative ‘middle position’ between two extreme, unacceptable answers: empirical idealism, which takes the requirements of a rule in any given situation to be constituted by our reaction to the case; and hard platonism, which takes these requirements to be delivered by unvarnished reality as absolutely the simplest or most natural way to (...) carry on. Tellingly, however, McDowell's position is itself unacceptably idealist in his picture of the way in which we are ‘involved’ on the right-hand side of biconditionals such as, ‘“Diamonds are hard” is true if and only if diamonds are hard’.In response to this stultifying state of affairs, I suggest that McDowell has followed the empirical idealist and hard platonist in assuming that the requirements of a rule must be grounded by something else: something external to the rule, which mediates between the rule and the standard for its correct application. This assumption is false. What is more, one application of a metaphor to which Wittgenstein has a somewhat equivocal relation—that of rules as rails invisibly laid to infinity—can help this point to stick. (shrink)