Earlier this week I appeared on a panel discussion hosted by the Heritage Foundation on ”The Conservative Mind at 60.” During the event I highlighted three themes that appear in Russell Kirk’s A Conservative Mind (published in 1953) and made the case for why those insights are still crucial to the health and wellbeing of modern conservatism.

As for the themes themselves, Dr. Kirk was a great proponent of prudence, so much so that he listed it among his canons of conservative thought. He wrote about the importance of recognizing that “change may not always be salutary reform: hasty innovation may be a devouring conflagration, rather than a torch of progress. Society must alter, for prudent change is the means of social preservation; but a statesman must take Providence into his calculations, and a statesman’s chief virtue, according to Plato and Burke, is prudence.”

Here is how the aforementioned Edmund Burke put it: “The lines of morality are not like the ideal lines of mathematics. They admit of exceptions, they demand modifications. These exceptions and modifications are not made by the process of logic but by the rules of prudence.”

So prudence – not pugilism, not purity – is the cardinal political virtue. Practical wisdom, practical judgment, the ability to take the appropriate action at a given place and time, was considered by the ancient Greeks, by Christian philosophers, and by statesmen like Burke and Lincoln to be of supreme worth and value.

A second theme that runs throughout The Conservative Mind is the importance of taking into account particular circumstances when applying political principles. Dr. Kirk pointed out that Burke based his every important decision upon a close examination of particulars. Burke detested “metaphysical politicians” and “abstraction” – by which he meant, according to Kirk, “not principle, but rather vainglorious generalization without respect for human frailty and the particular circumstances of an age and nation.” And so, Kirk argued, principles are necessary but they must be applied discreetly and with infinite caution to the workaday world.

This leads to a third set of insights by Kirk, which is that human nature suffers irremediably from certain faults; that to aim for utopia is to end in disaster; that we are not made for perfect things; and that all we reasonably can expect is a tolerably ordered, just, and free society. In other words, we should not expect perfection in a fallen world – not from us, and not from others.

Which brings me to the here and now. There exists what might be called a conservative temperament. To be sure, such a temperament doesn’t preclude one from engaging in debates, with passion and conviction, to advance what one believes to be right. But what I do think is problematic are those who desire to excommunicate from the ranks those they perceive as apostates.

What do I have in mind? One example is the targeting of Representative Pete Sessions of Texas. As this article makes clear, Sessions, a rock-solid conservative who has a 97 percent lifetime rating from the American Conservative Union, is under assault from a super PAC, the Senate Conservatives Fund, for being a “Texas RINO” (Republican in Name Only) and a “wishy-washy” Republican who is willing to “destroy our freedoms.” And what is the grave and unforgivable offense committed by Sessions? He opposed the effort by Senators Ted Cruz, Mike Lee, and others to shut down the government if the Affordable Care Act isn’t defunded. (As the Wall Street Journal points out in this editorial, this gambit is premised on the belief that “if the House holds ‘firm’ amid a shutdown, then the public will eventually blame Mr. Obama and the Democrats, who will then fold and defund ObamaCare.” Which is about as likely as yours truly becoming the starting center for the Miami Heat next year.)

This excommunication impulse is becoming increasingly dominant within some conservative quarters. The issue is framed as a “litmus test” and conservatives are being told by prominent figures within conservatism that any Republican who votes against the Cruz strategy is not worth voting for ever again.

That position strikes me as injudicious. If a similar litmus test had been applied to Ronald Reagan when he was governor of California, when he signed into law a record tax hike and liberalized California’s abortion law, he would have been deemed insufficiently “pure” and unworthy of support.

Senators Tom Coburn, Jeff Flake, and John Cornyn – as well as scores of their colleagues in Congress – are hardly traitors to conservatism and the cause of self-government. They have not, in the words of a FreedomWorks fundraising e-mail, “betrayed you.” They simply opposed what they considered to be a bad (and fated-to-fail) idea. I believe they were right to do so; others obviously disagree. But the disagreement shouldn’t rise to the political equivalent of a capital offense.

People should be judged in the totality of their acts. And the effort to portray the Cruz maneuver as a litmus test dividing real conservatives from RINOs is misguided. On some fundamental level it is also, I believe, at odds with conservatism as understood by many of its greatest exponents. It’s time to return prudence to its proper place in the conservative pantheon.

Peter Wehner is a senior fellow at the Ethics and Public Policy Center.