Knowledge is at the heart of intelligent behaviour. The ability to obtain, manipulate and communicate knowledge, in explicit form, is what distinguishes humans from other animals. This suggests that any study of intelligent behaviour, theoretical or experimental, would have the same starting point, namely a Science of Knowledge, which studies the basic forms of knowledge, its acquisition, and its processing. Yet there does not seem to exist such a unified and mutually agreed science of knowledge. In ancient times philosophy, the 'love of knowledge', would aim to fulfil this role of the Mother of all Sciences, but philosophy has since long lost its central place and has mostly fragmented into specialised sciences such as physics, biology, and mathematics. Computer science, a relatively young branch on the tree of knowledge, has some aspirations to be the science of knowledge, but is currently at best a loosely connected collection of engineering technologies and abstract mathematical theory. Artificial intelligence -- the discipline studying fruitful connections between intelligent behaviour and computers -- would be another contender, but has been accused of overstating its claims, having unclear goals, and applying sloppy methodology. In this chapter I argue that logic, in its widest sense, is -- or at least, should be perceived as -- the science of knowledge.