Commonsense, I suggest, is that native practical intelligence by which men test the truth of knowledge and the morality and prudence of action. I suppose that we can use it to describe not only this faculty of testing, but the product of thinking; at least common usage seems to indicate that we may.
Now, this native intelligence is, I further suggest, an hereditary factor in a man; a factor raised or lowered by the activity or sluggishness of the thyroid or pituitary glands, or both of them, or by some other gland. Individuals with their glands adjusted in a certain way have commonsense or the faculty for testing, etc; those with their glands ill-adjusted have a lack of it. No census could ever reveal how many people have this faculty for prudent action, so there is never likely to be any way of determining whether any group of people, or any nation, will act with commonsense in any emergency, or in its legislative halls. This conclusion if sound is disturbing, but it explains a lot of things.
R.S. Maynard, ‘What is Commonsense’ (1934)
The word commonsense is, I fear, a bête noire of philosophers, partly because it is used and quoted to defy their theories, and partly because it is very difficult to find any clear or precise meaning in its usage. I do not mean by it what may be called horse-sense, nor is it to be confined to sense knowledge, still less to public opinion. The word is chosen as convenient to express and cover certain activities of the mind and their content, which can, I think, legitimately be put under one category. By sense is understood what comes by way of experience. Experience, however, is also a vague word, and so I mean by it and sense what can be classed under perception, direct knowledge and judgement; all, in fact, that is opposed to speculation or reflective thought. I should add that in the use of these terms so far, no particular theory is insinuated; they are words of everyday use, and are intended to be taken according to that use.
The adjective “common” limits the kind of “knowledge” contained under “sense”, and again it is useful as excluding the ephemeral the conventional, the technical, and the trivial. There is a common stock of knowledge which all men and women use in the ordinary concerns of life gained from the primitive and inevitable experiences which every human being must undergo. This common experience is found in language, and used in literature and conversation, and presupposed and added to in the conduct of art and commerce. Were there no such commonwealth of meanings, language could never have become the easy means of communication that it is, and we should be perpetually in a worse plight than the builders of the Tower of Babel. When we are puzzled, as to-day, by certain modern writers of a new prose or Futuristic art, the cause is a conflict of a new set of meanings created by a theory with the old and established, and the latter will win the day unless the new can rid itself of the esoteric and show itself a legitimate development of what is sound in tradition.
M. C. D’arcy, ‘The Claims of Commonsense’ (1927)