  At one level, this line of argumentation is part of an argument for the existence of God. But, at another level, it is an effort to demarcate the proper object of the human mind as being and to point out that, if we reflect upon the notion of being (ens) in terms of its actuality (esse) we are inexorably led to the conclusion that there is a Perfect  Being.[31]  We reach the same kind of conclusion if we reflect, not upon the primary object of the mind, but upon its operations. The certainty of judgment requires that we be aware of the impossibility of our being mistaken combined with our awareness that the truth that we know cannot be otherwise; indeed, the most fundamental truths we know are all immutable. But, following Augustine, Bonaventure claims that there is no source for immutable truth other than God, since God is the only immutable and unchanging  Being.[32]