Externalism about some mental property, M, is the thesis that whether a person has M conceptually depends, in part, on the person's environment. Architecturalism about M is the thesis that whether a person has M conceptually depends, in part, on the person's internal cognitive architecture. I consider a number of arguments of the form (MC):(1) I have mental property M;(2) If I have mental property M, then I meet condition C; Therefore, (3) I meet condition C . . . 

These arguments are potentially problematic to the extent that premise (1) can be known with first‐person authority and premise...

Externalism about some mental property, M, is the thesis that whether a person has M conceptually depends, in part, on the person's environment. Architecturalism about M is the thesis that whether a person has M conceptually depends, in part, on the person's internal cognitive architecture. I consider a number of arguments of the form (MC):(1) I have mental property M;(2) If I have mental property M, then I meet condition C; Therefore, (3) I meet condition C . . . 

These arguments are potentially problematic to the extent that premise (1) can be known with first‐person authority and premise (2) can be known by way of a philosophical argument for an externalist or architecturalist thesis. For, in that case, knowledge of both premises can be had without rising from the armchair, and there is a transparently valid argument from these premises to the conclusion (3). Yet it is intuitively implausible that I have a non‐empirical route to substantive knowledge about my environment or about my cognitive architecture.

I suggest that we can avoid this problem of armchair knowledge if we allow that there are principles that limit the transmission of epistemic warrant from the premises to the conclusion of even palpably valid arguments.