HUME TO HEGEL Hume and others, as we have seen, had tried to for the philosophy of mind what Newton had done for the philosophy of bodies, making the association of ideas the psychic counterpart of gravitational attraction between bodies Kant’s programme for rendering metaphysics scientiWc was on a more ambitious scale Philosophy, he believed, needed a revolution like that of Copernicus who had moved the earth from the centre of the universe to put the sun in its place Copernicus had shown that when we think we are observing the motion of the sun round the earth what we see is the consequence of the rotation of our own earth Kant’s Copernican revolution will for our reason what Copernicus did for our sight Instead of asking how our knowledge can conform to its objects, we must start from the supposition that objects must conform to our knowledge Only in this way can we justify the claim of metaphysics to possess knowledge that is necessary and universal Kant distinguishes between two modes of knowledge: knowledge a priori and knowledge a posteriori We know a truth a posteriori if we know it through An engraving of Kant at the age when he published his first Critique 102