The metaphysical instinct has its origins in our awareness of contingency – the contingency of both ourselves and everything that is not ourselves. This instinct, this awareness, is responsible for some of the great creative minds in the natural sciences, as Stanley Jaki has argued quite powerfully. What the metaphysical instinct does most profoundly, though, is to compel us from the contingent to the necessary – this seems to be something over which we have little positive control (though we are quite capable of resisting and distorting this instinct). Reality itself, contingent as it is, points to and compels us towards the non-contingent – if we are in contact with reality in any meaningful way, then sooner or later this instinct will lead us to the necessary.
The metaphysical instinct, though it leads us to the necessary, does not lead us there necessarily. As I said above, this instinct can be resisted and distorted – a look over the history of philosophy will reveal the ideas which follow from this resistance and distortion. Positivism, rationalism, empiricism – all epistemological extremes. The metaphysical instinct compels us towards a middle ground, where our contact with empirical reality leads us far past the merely sensory.
If one grants that we are in contact with reality, a coherent, ordered universe of related things in their totality, then sooner or later, the metaphysical instinct will compel one to the necessary, the non-contingent, the Absolute, the explanation for the contingent reality with which we are in empirical contact. One can resist this instinct and the compulsion, but only at the price of sinking into mystery-mongering. To deny the metaphysical instinct and to resist the compulsion to the Absolute is to deny reality itself.