 A problem, of course, is that it would seem that a person would need to have an idea of God in order to have faith that God exists. Cavendish is clear that we can have an idea of the effects of God’s omnipotence, but she does not think that natural reason can have an idea of an immaterial itself. We can have an idea that there is a cause of these effects, but not an idea of what the cause is, or what it is that makes that idea and idea of God as opposed to something else. Cavendish might posit that we have supernatural and immaterial souls and that these can have an idea of God, but the question again is how she would be entitled to make suppositions about immaterial souls. One of her aims in circumscribing the limits of natural philosophy is presumably to make room for faith, but there is a worry that she has gone too far in holding that we cannot have ideas of immaterials. As Descartes remarks,