Agnosticism, in fact, is not a creed, but a method, the essence of which lies in the rigorous application of a single principle.... Positively the principle may be expressed: In matters of the intellect, follow your reason as far as it will take you, without regard to any other consideration. And negatively: In matters of the intellect, do not pretend that conclusions are certain which are not demonstrated or demonstrable.

The Essence of T. H. Huxley: Selections Form His Writings (ed. 1967)