Wherein is explained the first principle, the existence of God, and the derived principles based upon it and following from it, which every one professing a religion should believe. As we said in the first book, the secondary principles which are based upon the existence of God are four: unity, incorporeality, independence of time, freedom from defect. In order that these derivative principles may be made clear, we must first explain the fundamental principle from which they are derived, namely the existence of God. Then we shall explain the derived principles one by one, that we may know how many there are.

Before doing this, however, I shall preface an Observation which is essential for every one who reads this book.