====== A Priori/A Posteriori ======

An evolutionary perspective gives insight into a traditional philosophical problem of the relation between //a priori// knowledge (which can be known to be true without reference to evidence from the world) and //a posteriori// knowledge (which can only be evaluated by examination of the world to see if it is in fact that way.)  This is closely related to the duality of necessary/contingent (see [[wp>A priori and a posteriori]]).   Our point here is that this somewhat dusty philosophical debate can be seen as related to still-vital concerns of human nature and how the mind works.

A trivial way that something might be known //a priori// is if the statement is a tautology ("All bachelors are unmarried"), but we find more interesting Kant's original speculations about the //a priori// structure of the mind (see [[wp>Immanuel_Kant#Categories_of_the_Faculty_of_Understanding | Categories of Understanding]].)  As we see it, Kant was basically right that the mind contains particular capabilities for perceiving kinds of order in the world, such as causation.

His argument was that these capacities of perception were //a priori//, somehow innate in man, perhaps God-given, or at least a necessary precondition for rational thought.  This is in a narrow sense correct.  When the philosopher sits down in his armchair, he does possess all of these capacities.  However, this neglects both the philosopher's life-history and the evolutionary history of his species.  From the evolutionary perspective, we see that our capacities of mind are a consequence of the usefulness of those capacities //in the world we happen to live in//. 

Kant's argument that the mind places a basically arbitrary structure on the world raises the possibility that our perceptions may be deluded, or likely at best grossly oversimplified.  This is to some degree true, in that we can only perceive a tiny fraction of what is "out there" (see [[analysis:physical:sensory_limitations]]) and our understandings of the world may be quite wrong at times (see [[analysis:mind:naive_realism]]), but evolution has guaranteed some alignment between the relevant properties of the actual world and our mental capacities of perception.

Although Kant's understanding of the problem of mind is firmly rooted in philosophical [[wp>Idealism]] (a belief that important truths can be discovered by thought alone), from an empirical scientific perspective, we argue that he made the mistake of assuming that whatever he could determine by introspection was necessary //a priori//.  He accurately introspected important aspects of the mind, but such capacities are only necessary from an [[wp>>Anthropic principle | anthropic]] perspective.  They are a precondition for the existence of philosophers, but philosophers didn't have to exist.

The question of [[analysis:evolution:nature_vs_nurture]] can be seen as another related aspect of the philosophical debate between [[wp>Idealism]] and [[wp>Empiricism#British_empiricism | empiricism]].  Kant's proposal of the //a priori// structure of the mind was a reaction to claims by empiricist philosophers such as [[wp>John Locke]] that the mind is a blank slate at birth ([[wp>Tabula rasa]], [[books:blank_slate]].)

{{tag>philosophy mind nurture}}