Principle of Sufficient Reason

The principle of sufficient reason, credited to Leibniz, suggests that there should be an answer to every reasonable question about why the universe is as it is. Everything should have a knowable cause. Yet this faith may be no more than wishful thinking, whose success as an evolutionary strategy in ordinary realms bears no guarantee that it applies universally, particularly in unfamiliar realms. In a weak sense, it may say no more than that human beings are capable of inventing a story to account for every observation. In a stronger sense, it asserts that there is a one-to-one correspondence between thought and reality—between map and territory—even between mathematical models and the real systems they model. In other words, it implies the pre-established harmony. This rigorous correspondence is not possible, however, unless the map is the territory or the territory is nothing but the map itself. For, the very nature of maps is that they are selective and symbolic representations, not literal duplications of the world. The principle of sufficient reason expresses the rationalist faith that the world should be knowable–and mathematically expressible—in any detail. It lies, for example, behind Eintein’s insistence on “completeness” for physical theories, such as the quantum theory. It underwrites the search for a definitive theory of everything. This faith is misplaced, however, if the world is actually real.