Descartes’ Criterion of Truth and the Existence of God
Descartes’ Criterion of Truth
One idea is clear when it is present and manifest to mindfulness. If we accept as true only what is presented clearly, we will never be wrong. Different is the idea that my consciousness is well defined in outline, not mixed with any other.
Moreover, we must be careful with the word “think” (and with the proposition “I think, therefore I am”) because with it we now refer to the experience through which we have a conceptual and intellectual knowledge of reality. However, for Descartes, it is more generic and becomes synonymous with any mental act, or experience, or mental or psychic content. Any mental act has the characteristic of being certain; none of them may be false. So it would be valid to say, “I remember, therefore I am,” “I imagine, therefore I am,” “I wish, therefore I am,” “I suffer, therefore I am,” just as much as “I think, therefore I am.”
Criterion of Truth: Clarity and Distinctness
The cogito is going to become a criterion of truth. In the proposition “I think, therefore I am,” there is nothing to ensure its truth except that it becomes clear that to think is necessary to exist. So we can take the general rule that “the things we think more clearly and more distinctly are all true.”
God as Guarantor of the Criterion of Truth
Anyway, this “criterion of truth” has no full guarantee until the existence of God and His goodness are proven. So far, Descartes has only demonstrated the existence of the thinking subject, but not of bodies, nor of God. This is what is proposed below. The divine veracity guarantees that I am not mistaken in thinking that those propositions are true that I conceive clearly and distinctly.
Demonstrating the Existence of God
The Argument from Perfection
If I, as I doubt (I know), am imperfect and I have the idea of perfection, it cannot come from me because the imperfect cannot create the perfect. Therefore, the idea of perfection must come from a perfect being, which is outside me, not me. This perfect being who implanted in me the idea of perfection is God because I have ideas of other things outside me (heaven, light, …) that currently are only thoughts; he still has not been found to occur and are no more perfect than me. It is thus demonstrated that the existence of God, and also the subject, depends on God.
The best known of the three proofs of the existence of God that Descartes offers is the ontological argument. This argument rests on the proof for the existence of God from the idea of God as a being absolutely perfect. In essence, this argument holds that conceiving of God is almost the same thing as thinking that God already exists. The idea of God already contains His existence, just as the idea of a triangle contains the fact that the sum of its three internal angles equals two right angles.
Demonstrating the Existence of Extended Substance
Once we have a criterion of truth and that it is guaranteed by God, which effectively means that the infinite substance guarantees the ability of human reason to find the truth (whenever you use the rational method properly), the French philosopher can address the existence of corporeal realities. It is beyond any doubt that I own ideas about reality outside my mind. It is unlikely that my thinking is the cause of them, nor does God intend to deceive me by putting in my mind ideas as coming from such things. Therefore, there must be material realities outside of my body that cause those ideas. However, the criterion of clarity and distinction does not guarantee me anything more than those objective qualities of bodies such as extension, motion, shape, location, duration, or number, but not those secondary or subjective qualities such as taste, odor, or temperature.
Structure of Reality: The Three Substances
For Descartes, there are as many substances as clear and distinct ideas your mind can conceive. Thus, the substance is the immediate subject of any attribute from which we get a real idea. There are therefore three substances: God (or the infinite or divine substance), thinking substance (res cogitans), and extended substance (res extensa). Now, what we perceive is not the substance as such, but attributes of substances. An attribute is that by which a substance is distinguished from another and is thought by itself. The attributes depend on the substance and are immutable. The essential attribute is the nature of a substance. Each substance has an essential attribute: thinking (res cogitans), perfection (God), extension (res extensa). The essential attributes are identified with the substance.
Cartesian thought is included in the mechanistic context: admitting only quantity, number, and local motion. It excludes any forces other than mechanical ones (i.e., the production of motion) and denies purpose. Descartes’ mechanism applies to the life of plants and animals, which he considers as mere automata without consciousness. It is led by their strict separation between the res cogitans and res extensa. So, in the case of a man, there is no given substantial union because the attributes of the two substances that compose him are different from each other. Man is a substance composed of two incomplete substances, but entirely complete. Ultimately, in the case of these two separate substances, the body is nothing but a machine coupled to the spirit, or, if preferred, the relation of mind to body is similar to that which exists between the pilot and the ship.
Ideas and Examples of Ideas
Finally, we will dedicate a line to the Cartesian conception of ideas, very different from the Platonic. For the Athenian philosopher, ideas were outstanding entities existing in an ideal world, separate from the physical and mental. For Descartes, ideas are representations (content) of the mind and can be of three types:
- Innate: Those that possess any prior experience or contact with the world. They have been implanted in our minds by God. These include, besides the idea of infinity or God, the idea of substance, knowledge of mathematical concepts and universal logical principles, and, of course, our knowledge of the laws of physics. Somehow we are born with a basic logic that allows us to learn and know the universe and God.
- Factitious: Those ideas that are figments of our imagination. The mind constructs them from other ideas. An example would be the mythical Pegasus.
- Adventitious: The ideas that are more or less faithful copies of reality lodged in my mind (feelings, images, and concepts) that I have obtained through the perception of the world.