Cognitio Naturalis de Deo (Natural Knowledge of God) is a lecture by John Duns Scotus from his Opus Oxoniense (or Ordinatio, 1298-1304). He provides arguments for and against the proposition that human knowledge of God is possible.

The first argument which is provided by Duns Scotus against the proposition that human knowledge of God is possible is that God cannot be perceived by sensory perception. If God cannot be perceived by sensory perception, then knowledge concerning God's attributes may not be possible.

The second argument against the proposition that human knowledge of God is possible is similar to the first argument, in that Duns Scotus argues that due to the limitations of human sensory capability, God is imperceptible to the senses, just as many natural phenomena are imperceptible to the senses.

A third argument against the proposition that knowledge of God is possible is that infinite being cannot be apprehended by the human intellect. If God is infinite, then human beings may not be capable of knowing God. If it is impossible for the human intellect to know an infinite number of things, then the human intellect may not be capable of comprehending the infinite nature of God.

Duns Scotus then approaches the question of whether knowledge of God is possible by asking whether we may attain knowledge of what God is not. He explains that we may deny that a given attribute belongs to God only if that attribute is contradictory to some other attribute which we have already affirmed as belonging to God. Any supposed negation of God thus presupposes, or depends on, a genuine affirmation of God.

Duns Scotus argues that there is no logical reason for trying to distinguish between knowledge of God’s essence and knowledge of God’s existence, because God's essence and existence cannot be separated from each other. To attain knowledge of God's existence is to attain knowledge of God's essence, and to attain knowledge of God's essence is to attain knowledge of God's existence.

According to Duns Scotus, it is possible for us to know some of the attributes of God without having an adequate concept of God. We cannot have an adequate concept of all of God’s attributes, because these attributes are infinite and are beyond the power of the human intellect to comprehend.

Duns Scotus provides several arguments in support of the proposition that human knowledge of God is possible, including the argument that we may be certain that God exists even though we may be uncertain as to whether God is finite or infinite.

Another argument for the proposition that human knowledge of God is possible is that the concept of God could not present itself to the intellect unless God actually existed, and therefore the concept of God must be based on knowledge of the existence of God. The intellect may not be able to form a concept of anything unless there is something to cause the intellect to apprehend an image or representation of that thing, and thus whatever causes this image or representation to be apprehended by the intellect must already exist. Concepts may be true or false, but may not be produced by the operation of the intellect alone without a corresponding image or representation of something. There must be an external reality to produce a concept of something.

Another argument for the proposition that human knowledge of God is possible is that God is perfect, and that therefore the concept of perfection implies that God is capable of being known.

Another argument for the proposition that knowledge of God is possible is that if the human intellect may properly conceive of any attribute of God, then the intellect may know God. If the human intellect may properly conceive of any attribute of God, then it may be able to properly conceive of many attributes simultaneously, and may be able to imagine a concept of God that would properly refer to to all of God’s attributes.

Another argument that human knowledge of God is possible is that the human intellect may be able to abstract an idea from any object which is presented to it by sensory perception. Thus, the intellect may be able to consider what is common to objects which can or cannot be perceived by the senses. Even if God cannot become an object of sensory perception, the intellect may be able to abstract an idea of God from all the objects which are presented to it by sensory perception, and thus valid knowledge of God may be possible.

Another argument that knowledge of God is possible is that even if all of God's attributes cannot be known by a finite mind, this fact does not mean that all of God's attributes cannot be known by an infinite mind. There may be a mind or a mode of reasoning of which we are not aware which may provide valid knowledge of God.

Even if some of these arguments for the possibility of human knowledge of God are accepted as valid, there still remains the question as to whether infinite being can be known by the finite intellect. Duns Scotus argues that knowledge of infinite being does not imply that the act of knowing is itself infinite unless the act of knowing fully comprehends the object of knowledge. It is not necessary for the act of knowling to share the same mode of reality as the object of knowledge, since an act of knowing which is by nature finite may properly correspond to an object of knowledge which is by nature infinite.

Duns Scotus admits, however, that because the human intellect is finite, human beings are not capable of a comprehensive act of knowledge in relation to an infinite object.

Regarding the question of whether God is knowable by identification of singular or individual attributes, Duns Scotus argues that the singularity or individuality of any attribute of God does not prevent us from abstracting a common concept from it. Though every attribute of God may be singular, every attribute may still be conceived as revealing universality. Everything that exists is in God.

A problem with many of Duns Scotus’s arguments for the possibility of human knowledge of God is the premise that we may know God by making the attributes of God the objects of our knowledge. It may be argued, to the contrary, that the attributes of God transcend any attempt to objectify them. We may not be able to make the attributes of God the objects of our knowledge, because God may transcend objective enquiry.

Another problem with Duns Scotus's approach to the possibility of human knowledge of God is that many of his arguments do not consider the relation between knowledge and faith. It may be argued that human knowledge of God is so limited that we cannot establish by either reasoning or sensory experience an adequate concept of God. Thus, knowledge of God may require faith.

Duns Scotus addresses this problem when he says that we may not be able to establish by reasoning alone any concept of God which corresponds to all of the necessary attributes of God, and that knowledge of these attributes may thus require faith in God./P>

Duns Scotus, John. "Cognitio Naturalis de Deo," in Duns Scotus: Philosophical Writings, edited and translated by Allan Wolter. Edinburgh: Thomas Nelson and Sons, Ltd., 1962.