According to Thomas Reid, powers of will and powers of understanding are distinguishable in thought, but conjoined in practice. This paper examines the claim that there is no inert intelligence, the operations of the understanding involving some degree of activity. The question is: whose activity? For it is clear that a great deal of our mental activity is not in our power. We need to distinguish between a weak and a strong sense of 'power', and consider our dependence 'upon God and the laws of nature' in our mental exertions.