'The problem of the Trinity is the mysterious union of the divine and human natures of Christ. Likewise, when we debate whether a mechanism – such as a fly drawn to the smell of meat, or a trap, or an arithmetickal engine – is thinking by itself, or merely displaying the ingenuity of its creator, we are asking whether or not those engines have, in some sense, been imbued with an incorporeal principle or, vulgarly, spirit that, like God or an angel, possesses free will.'