Key Arguments

• Locke introduces this as 'the fourth sort of our knowledge, viz. of the real actual existence of things'.
• He affirms that 'we have an intuitive knowledge of our own existence', echoing his earlier claim that the mind’s consciousness of its own thinking provides immediate certainty.
• He states that we have 'a demonstrative knowledge of the existence of a God', which he elsewhere argues for via a causal demonstration from our own existence.
• He sharply limits our knowledge of other existences: 'of the existence of anything else, we have no other but a sensitive knowledge; which extends not beyond the objects present to our senses.'
• Thus the three previously distinguished degrees of knowledge—intuitive, demonstrative, and sensitive—are each assigned a specific domain of real existence: self, God, and presently perceived external objects.

Source Quotes

Of the three real existences of which we have certain knowledge. Fourthly, As to the fourth sort of our knowledge, viz. of the real actual existence of things, we have an intuitive knowledge of our own existence, and a demonstrative knowledge of the existence of a God: of the existence of anything else, we have no other but a sensitive knowledge; which extends not beyond the objects present to our senses. 22.

Key Concepts

• Fourthly, As to the fourth sort of our knowledge, viz. of the real actual existence of things
• we have an intuitive knowledge of our own existence, and a demonstrative knowledge of the existence of a God
• of the existence of anything else, we have no other but a sensitive knowledge; which extends not beyond the objects present to our senses

Context

Book IV, Chapter III, §21, where Locke briefly recapitulates how the three degrees of knowledge (intuitive, demonstrative, sensitive) apply to the knowledge of real existence.