Certainties and ineffable knowledge
It is important to distinguish between certainties as background elements that are constitutive for a certain (set of) practice(s); and ‘ineffable’ knowledge, such as knowing what a game is, how a clarinet sounds. These are really two different kinds of cases, and they should be kept apart. The latter are active within a language game, they can be conveyed, taught, tested; only not by means of explicit definitions and descriptions. The former are not active, but constitutive; they are not taught, not tested.