This paper argues that Descartes and Hume ought to be viewed as pioneers of cognitive externalism. However, externalism old or new faces some serious challenges. The second part of the paper enlists the empirical resources of recent works in psychology and neuroscience to argue for a thoroughly externalist view that meet the challenges. The view includes such claims as perceptual and fast thinking knowledge ought to be viewed separately from theoretical or slow thinking knowledge; the former falls into a Humean, the latter Cartesian, type externalism.