Mainstream epistemology seeks necessary and sufficient conditions for the possession of knowledge. The focus is on folksy examples and counterexamples, with reasons undercutting reasons that undercut reasons. According to epistemic reliabilism, reasons may be sustained, truth gained and error avoided if beliefs are reliably formed, sometimes in the actual world, sometimes in other worlds too. But the stochastic notion of reliability unfortunately backfires, reinviting a variety of skeptical challenges.

Mainstream epistemologies emphasizing reliability date back at least to the 1930s, to F. P. Ramsey's (1931) note on the causal chaining of knowledge. The nomic sufficiency account developed by Ramsey and later picked up and modified by Armstrong in the 1970s is roughly as follows: If a connection can be detected to the effect that the method responsible for producing a belief is causally chained to the truth due to the laws of nature, then this suffices for nomologically stable knowledge and keeps Gettierization from surfacing. Causality through laws of nature gives reliability (Armstrong 1973).

Armstrong draws an illuminating analogy between a thermometer reliably indicating the temperature and a belief reliably indicating the truth. Now a working thermometer is one that gives accurate readings in a range of temperatures. This is not a coincidence. A thermometer is successful because there are laws of nature that connect the readings to the very temperature itself.