Garrigou-Lagrange argues against nominalism and subjective conceptualism by emphasizing the necessity of metaphysical realism. He criticizes nominalism for reducing intellectual knowledge to sense knowledge, which leads to the denial of the ontological value of dogmas. He also attacks subjective conceptualism, like Kant's, for its denial of the objectivity of the intellect's relation to being, which results in irrationality and absurdity.
In defense of metaphysical realism, Garrigou-Lagrange asserts that the intellect's object is being, and that the formal object of the intellect is being, not color, sound, or consciousness. He argues that the intellect perceives divisions in being, such as subject and object, potency and act, which are necessary for understanding multiplicity and becoming. He claims that metaphysical realism is superior to both nominalism and subjective conceptualism, as it provides a comprehensive and precise affirmation of the fundamental law of thought and being, the principle of identity or non-contradiction.