This is the epistemological problem, and it was a very fundamental one, but of course – as behind all problems in philosophy and theology – it is always the problem of God which is decisive, and so I now go to the doctrine of God in medieval thinking, and I come again partly to these three men of the 13th century.
The medieval idea of God has three levels: 1) The first and fundamental level is the idea of God as primum esse, the first being, or prima causa, the first cause. By “cause” here is meant not as “cause and effect,” as we have it in the realm of finitude – the word “prima,” “first,” means not the first according to time, but the ground of all causes, so that the term “cause” is here used more symbolically than literally. It is the creative ground in everything, creatrix universa1ium substantia, the creative substance of everything that is. This is the first statement about God. He is the Ground of Being, as I like to express it, or being itself, or the first cause – all these terms point to the same meaning.
2) This substance cannot be understood in terms of the inorganic realm – for instance, as an inorganic substance like fire or water, as the old physicists did – nor in the biological situation, as a life process, but it must be understood as intellect.
The first quality of the Ground of Being is intellect. Intellect doesn’t mean intelligence, but it means the point in which God is for Himself subject and object at the same time; or, as it was carried through, God knowing Himself and knowing the world as that which He is not. The Ground of Being, in other words – the “creative substance” – is a bearer of meaning. The world – this is the consequence – is meaningful, can be understood in words which have meaning. The logos, the word, can grasp it. In order to understand reality, we must presuppose that reality is understandable; and reality is understandable because the Divine ground has the character of intellect. Only because the Divine intellect the ground of everything, is knowledge possible.