  4. Transcendental arguments involve transcendental claims, to the effect that X is a necessary condition for the possibility of Y, where in saying this, the arguments do not assume this to be a matter of merely causal or natural necessity. Given that their target is the skeptic who challenges our claims about the world, there are clearly two good reasons for this. First, although our observation of the world might suggest that experience has certain necessary causal conditions (e.g., light and sound must be transmitted between particular wavelengths), we can hardly use such considerations against a skeptic of this sort, for whom all such empirical knowledge is in question, and against whom we are therefore required to adopt a position that is less open to doubt in this way. Second, if the transcendental argument’s claim is one of only natural necessity, then this allows that there are possible worlds (for example, where the laws of physics do not hold) in which this claim is false, again opening us up to the skeptical challenge of showing we are not in such a world.