In 1950, literary critic Lionel Trilling had occasion to comment that “nowadays there are no conservative or reactionary ideas in general circulation.” He went on to observe that while the “conservative impulse” was alive and well, it tended to express itself not “in ideas but only in … irritable mental gestures.”

Of course, even as Trilling was penning these lines, a genuine renaissance in conservative thought was under way. The giants of modern American conservatism, from F.A. Hayek to Leo Strauss to Eric Voegelin, were just getting warmed up. The “new conservatism” of Peter Viereck, Russell Kirk, and William F. Buckley Jr. was being formulated, to be followed a decade or so later by the “neo-conservatism” of Irving Kristol, Norman Podhoretz, and James Q. Wilson. And all these ideas had consequences, as could be seen in the changing face of the Republican Party. The party of liberal Republicanism, of Dwight Eisenhower and Nelson Rockefeller, became in little time the conservative party of Barry Goldwater, Ronald Reagan, and Newt Gingrich.

Yet for all of its intellectual power and political success, conservatism – or really a small corner of it – could never quite outgrow the “irritable mental gesture.” Stephen J. Tonsor is a case in point.

Not many people will be familiar with Mr. Tonsor’s name, which is unfortunate, for he has a keen mind and sharp wit. Until his retirement, he taught history at the University of Michigan in Ann Arbor, where he was highly regarded as a teacher and mentor. For many conservative students in particular, his classroom was an oasis of genuine thought and learning. The Intercollegiate Studies Institute (ISI) has just published a collection of his essays, “Equality, Decadence, and Modernity” (350 pages, $30); it displays Mr. Tonsor’s many virtues as a thinker but also traditional conservatism’s tendency to degenerate into crankiness.

Mr. Tonsor is a self-described paleoconservative and reactionary. As an intellectual tendency, paleoconservatism is at war with modernity. Paleocons are less conservators of the American tradition than counterrevolutionaries, who end up issuing calls for, as one of their leading theoreticians once did, “radical opposition to the regime.”

Characteristic of this kind of politics is Patrick Buchanan’s magazine, the American Conservative, which stridently opposed the war in Iraq, despises Wal-Mart capitalism, and is utterly frank in its hatred of Jews. Not surprisingly, its editors split on whether to endorse George W. Bush in the 2004 election. Despite its name, the American Conservative has far more in common with the left-wing Nation than the conservative National Review. The political extremes, it seems, always find common cause.

Many of the major themes of paleoconservatism are on display in Mr. Tonsor’s writings. The political meaning and consequences of modern decadence are among his central preoccupations. So, too, is the question of equality. Of the Declaration of Independence’s assertion that “all men are created equal,” Mr. Tonsor remarks, “Surely its meaning must be attenuated and diluted by the facts of life as described by the ethologists and sociobiologists.” “The Enlightenment in all its forms,” he avers, must be judged a failure.

Politically, Mr. Tonsor is vehemently anti-big government, believing that “beyond the needs of defense and a limited federal police power, only those extraordinary needs of national communication, the alleviation of national disaster, and the control of corporate entities that are national or international in scope should be left in the hands of the federal government.” In foreign affairs, he declares himself a “noninterventionist.”

Mr. Tonsor’s conservatism is rooted not in the American founding or even Edmund Burke but, as he describes it, in the political philosophy of Aristotle and Thomas Aquinas and the culture of Christian humanism. He calls his worldview “Roman or Anglo-Catholic.”

This view of conservatism never left much room for Jewish neoconservatives in its ranks. Indeed, Mr. Tonsor is best known for a barb he once aimed at neocons: “It is splendid when the town whore gets religion and joins the church. Now and then she makes a good choir director, but when she begins to tell the minister what he ought to say in his Sunday sermons, matters have been carried too far.”

According to the editor of the ISI volume, Gregory Schneider, Mr. Tonsor’s dislike for the neocons only hardened as he aged. A year ago Mr. Tonsor declared that “to be ‘neo’ is to live in danger. Mutant types in culture and in biology are … nearly always fatally flawed and prone to an early and ugly demise.” (Mr. Tonsor has always wielded a wicked pen – “Mr. Nixon,” he once wrote, “is not a swinger when compared to the Kennedy brothers, but then I doubt that he will have difficulties with an unlighted bridge.”)

Mr. Tonsor rather reminds one of Henry Adams: so soured on modernity that he is of little use in navigating its more dangerous eddies or understanding its actual accomplishments. The essays here collected are lively enough, but as a source for a decent and humane politics they come up short.

Mr. Wolfson is a consulting editor of Commentary and a senior fellow at the Ethics and Public Policy Center.