Harry Collins’s Tacit and Explicit Knowledge characterises tacit knowledge through a number of antonyms: explicit, explicable, and then explicable via elaboration, transformation, mechanization and explanation and, most fundamentally, what can be communicated via “strings”. But his account blurs the distinction between knowledge and what knowledge can be of and has a number of counter-intuitive consequences. This is the result of his adoption of strings themselves rather than the use of words or signs as the mark of what is explicit and, I suggest, it may stem from his earlier response to Wittgenstein’s rules regress.