Hume then examines probable reasoning under conditions of empirical uncertainty, distinguishing "proofs" (conclusive empirical evidence) from mere "probabilities" (less than conclusive empirical evidence). Beginning with a brief section on the "probability of chances", he gives the example of a six-sided die, four sides marked one way and two sides marked another way: background causes lead us to expect the die to land with a side facing up, but the force of this expectation is divided indifferently across the six sides, and finally reunited according to the die's markings, so that we end up expecting the one marking more than the other. This is mainly prelude to the "probability of causes", where Hume distinguishes three "species of probability": (1) "imperfect experience", where young children have not observed enough to form any expectations, (2) "contrary causes", where the same event has been observed to have different causes and effects in different circumstances, due to hidden factors, and (3) analogy, where we rely on a history of observations that only imperfectly resemble the present case. He focuses on the second species of probability (specifically reflective reasoning about a mixed body of observations), offering a psychological explanation much like that of the probability of chances: we begin with the custom-based impulse to expect that the future will resemble the past, divide it across the particular past observations, and then (reflecting on these observations) reunite the impulses of any matching observations, so that the final balance of belief favors the most frequently observed type of case. Hume's discussion of probability finishes with a section on common cognitive biases, starting with recency effects. First, the more recent the event whose cause or effect we are looking for, the stronger our belief in the conclusion. Second, the more recent the observations we draw on, the stronger our belief in the conclusion. Third, the longer and more discontinuous a line of reasoning, the weaker our belief in the conclusion. Fourth, irrational prejudices can be formed by overgeneralizing from experience: the imagination is unduly influenced by any "superfluous circumstances" that have frequently been observed to accompany the circumstances that actually matter. And paradoxically, the only way to correct for the pernicious influence of "general rules" is to follow other general rules, formed by reflecting on the circumstances of the case and our cognitive limitations. Throughout the section, Hume uses his "force and vivacity" account of belief to account for