Ordinary knowledge consists for the most part of mere opinions or beliefs, more or less well founded. But it implies a solid kernal of geniune certainties
in which the philosopher recognises in the first place data of the senses (for example: that bodies possess length, breadth, and height
), secondly self-evident axioms (for example, the whole is greater than the part, every event has a cause, etc.
), and thirdly, consequences immediately deducible from these axioms (proximate conclusions). These certainties which arise spontaneously in the mind when we first come to the use of reason are thus the work of nature in us, and may therefore be called an endowment of nature as proceeding from the natural perception, consent, instinct, or natural sense of the intellect. Since their source is human nature itself, they are common to all men. They may therefore be said to belong to the common perception, consent, or instinct, or to the common sense of mankind. The great truths without which man's moral life is impossible - for example knowledge of God's existence, the freedom of the will, etc. - belong to this domain of common sense, as consequences immediately deducible (proximate conclusions) from primary data apprehended by the intellect. All men, unless spoiled by a faulty education or by some intellectual vice, possess a natural certainty of these truths.