Empiricism tries to avoid skeptical problems by restricting knowledge to what can be perceived by the senses. From early modern philosophers such as John Locke and David Hume to later thinkers such as Rudolf Carnap and Bas van Fraassen, the restriction of knowledge to sense experience has had strong appeal. I will show, however, that strict empiricism is incompatible both with the neuropsychology of perception and with the practice of science. Our brain processes are, fortunately,capable of reliably taking us well beyond what is presented to us by our senses.