The refined ability response — that Harpo acquires the ability to imagine or remember the nature of sound — only defers the problem rather than solving it.

There are at least two lines of response to this popular but controversial argument. First is the ‘ability’ response. According to this, Harpo does not acquire any new factual knowledge, only ‘knowledge how’, in the form of the ability to respond directly to sounds, which he could not do before. This essentially behaviouristic account is exactly what the intuition behind the argument is meant to overthrow. Putting ourselves in Harpo’s position, it is meant to be obvious that what he acquires is