Drawing the complex terrain of the theories of induction and of the various ways to ground inductive knowledge in the middle ages is the aim of this paper. There have already been two excellent attempts to draw this terrain. The first is by Julius R. Weinberg and the second by E. P. Bos. My attempt differs from theirs in two major respects. The first is that it is more detailed in the examination of the various theories and their relations. The (...) second is that I focus on the role of natural necessities in induction. In particular, I try to place the various conceptions of induction within a network of issues that relate to the problem of universals, natural necessities and a power-based approach to activity in nature. Here is the road map. Section 2 explains Aristotle’s views of induction, as this were mainly developed in Posterior Analytics Book II.19 and states what I take it to be the main dilemma of induction, as this was described by Sextus Empiricus: induction is either perfect and impossible or imperfect and unjustified. In section 3, I move to Thomas Aquinas and his own attempt to justify induction and the actuality of general and necessary principles based on experience by an appeal to the natural light of reason. In section 4 I discuss John Duns Scotus’s reliance on a self-evident maxim to bridge the gap between imperfect and perfect induction. Section 5 moves to William of Ockham ’s peculiar attempt to justify single-instance inductions. Then, section 6 offers a detailed account of Jean Buridan’s ground-breaking re-conceptualisation of induction and the role of intellect in it. Section 7 discusses the critique of induction by Nicolaus of Autrecourt. Finally, section 8 offers a brief account of Pseudo-Scotus’s move from knowledge to opinion. (shrink)