The problem of induction is the philosophical issue involved in deciding the place of induction in determining empirical truth. The problem of induction is whether inductive reason works. That is, what is the justification for either:

1. generalizing about the properties of a class of objects based on some number of observations of particular instances of that class of objects (for example, "All ravens we have seen are black, and therefore all ravens are black"); or
2. presupposing that a sequence of events in the future will occur as it always has in the past (for example, the attractive force described by Isaac Newton's law of universal gravitation, or Albert Einstein's revision in general relativity).

Francis Bacon, Isaac Newton, and numerous others up until at least the late 19th Century have considered inductive reasoning the basis of scientific method—indeed inductive reasoning is used today, though in a more balanced interaction with deductive reasoning and abductive reasoning. By the inductive approach to scientific method, one makes a series of observations and forms a universal generalization. If correct and stated in a sufficiently accurate way, an inductively arrived at statement relieves others of the need for making so many observations and allows them to instead use the generalization to predict what will happen in specific circumstances in the future. So, for instance, from any series of observations that water freezes at 0°C at sea-level it is valid to infer that the next sample of water will do the same--but only if induction works. That such a prediction comes true when tried merely adds to the series; it does not establish the reliability of induction, except inductively. The problem is, then, what justification can there be for making such an inference?