I often hear or read Common sense isn't common. or, ambiguously, Common sense isn't.

The term common sense refers to variety of things believed or formerly believed to be closely related. In some cases, the term is indeed a description; in others, it is like Common Raven, which began as a description or as an attempt at a description, but names a now uncommon bird.

Consulting the SOED, I find about five definitions of common sense. Archaically, common sense refers to a supposed faculty that coördinated and united senses such as those of sight and of touch to form impressions of the world. The term may refer to ordinary or normal understanding (which must be common). Common sense may also refer to collective judgment across some group of people. Philosophers may use common sense to refer to the power by which generally accepted beliefs are formed in the absence of contemplation and of instruction. Normatively, common sense refers to reliable practical wisdom in everyday matters.

I don't use the term common sense much at all, but I occasionally use it normatively, as when I tell people that an introductory course in microeconomics will start with building-blocks of common sense but assemble them with uncommon care. Now, I suppose that I could use those very same words without normative intent, but I really am hoping that the audience will accept the blocks as themselves reliable. I cannot teach my audience everything, and I shouldn't have to teach those blocks to them.

When I use common sense normatively, the notions that I have in mind are of sound reasoning that is within the intellectual capabilities common to human beings, and of the structures of belief that result from such application. Something that would not be what I were normatively calling common sense would be unsound or outside of the possibility of common understanding. However, I'm more likely to say That should be common sense. than That seems like common sense. I'm even more likely to say That should be obvious.

I'm on the subject of common sense because various people in various groups will treat beliefs as if they are obvious to everyone who is not a fool when they are no such thing. Treating them as common sense — here using common sense normatively — is a form of implicit or explicit begging of the question; it is a violation of the rules of proper discourse. That said, most of those who treat those beliefs as common sense sincerely, thoughtlessly regard most of them as such; these people are not violating the rules willfully.

I've encountered this begging of the question by the political left, by the political right, and by political moderates. But I am at present most concerned by the misrepresentations from the left, because they have control of so much of the commanding heights of our culture. When a strong wind prevails, one leans against it, not against a wind of the past nor against a wind that may come in the distant future.

Examples of propositions that some or all of the left treat as common sense include

• that greater economic efficiency can often be achieved by replacing markets with state administration based upon centralized collection of relevant information;
• that material inequality is a social ill;
• that poverty may be reduced by state-directed redistribution of wealth or of income from the affluent to those of little means;
• that, if a school system is performing poorly, then some increase in the material resources provided to it would be sufficient to improve that performance, and that any decrease in such resources will be followed by a decline in performance.

Treating these propositions as common sense precludes consideration.

To impel consideration of all that the left distinctly takes to be common sense, we want a concise label for that group of their beliefs. We want an X such that we can say things such as This idea is X; if you're going to treat it as common sense, then you're first going to have to show that it truly is common sense. or such as This idea is X but it is not common sense; if you're going to justify it, then you're going to have to justify it on some other basis. Any label that itself begs the question, in some contrary way, will do little or nothing to promote thoughtful consideration. It will not provoke the left to think, and it will offend uncommitted members of the audience (with whom we should be principally concerned) and otherwise cause them to dismiss the argument as logomachy amongst knaves and fools. An insulting label would beg the question in an especially counter-productive way.

But the label should be used to establish a context of discourse across arguments and conversations in which context the left can no longer simply proceed with its presumptions as such or it will come to seem absurd to the audience and outmanoeuvred to itself. I don't know what the properly effective label should be.