Some six centuries before the Christian era began, the prophet Jeremiah lamented: “How doth the city sit solitary that was full of people.” That agile-minded social observer, Jane Jacobs, has written a jeremiad of sorts, but it is a muddled one. Her observations are as keen as they were in her influential take on urban planning, The Death and Life of Great American Cities. But in Dark Age Ahead she fails to marshal these observations in service of her thesis, that our culture is slouching toward a dark age.

Jacobs’ readable text argues that our society’s core institutions are in trouble. The nuclear family is failing, according to Jacobs, not because of some moral rot in us, but because neo-conservative fiscal policies have made running a household uneconomical. Jacobs doesn’t squarely address the economist’s truism, however: that coupling up reduces each individual’s living expenses, and that two-parent families are more cost efficient than single-parent ones.

She favours self-government for the learned professions, but her book makes the case for greater state supervision. The text adeptly shows how accountants in super-sized firms helped companies like Enron defraud the public, but the accounting profession was then, and remains, largely a self-governing one. The solution she proposes (stronger professional self-government) looks, by the evidence she presents, to be a part of the problem.

Similarly, Jacobs views science as being in decline. To help prove this she relates how one researcher was able to discern why so many people died during a power outage in Chicago, while an entire team dispatched by the Centre for Disease Control and Prevention failed to do so. But individuals who go against the herd have always been responsible for significant scientific advances. If the book is to convince us that real dark ages are in the offing, it must show that we are now abandoning our belief in reason’s power. On the basis of the same example, another observer might celebrate the sole researcher’s ability to discern the cause of the fatalities, finding him an inheritor of the Enlightenment.

Jacobs aptly observes that universities currently focus more on preparing students for the job market than on training their minds. But she fails to convince us that the academy is neglecting its mission, that it cannot simultaneously add dimension to the average mind and school the extraordinary intellect. In arguing this point, Jacobs could have followed the path beaten by Allan Bloom in The Closing of the American Mind. But Jacobs never comes to terms with the small-c conservatism that animates her own book and, accordingly, produces this curious creature: a hopeful, liberal-minded jeremiad. To be effective as a warning, a jeremiad’s author must embrace the premise that things were better in the past than they are now, and show us why. Jacobs doesn’t persuade us, because it appears from this text that she hasn’t really convinced herself that this is so.

The book is best when Jacobs returns to her forte, observing the city, charting its victories and losses. She makes short work of the junk science of traffic engineering, discrediting the widespread belief that road closures can’t reduce traffic. Her analysis of the problems that cities face in a federalist system is also masterful. In a key moment in the book, she recounts a discussion with Paul Martin – an informal chat that may indicate the limits of the prime minister’s newfound enthusiasm for the urban project. To prevent decline from turning into fall, Jacobs argues, Martin and his provincial counterparts will have to cede power to the cities, not just occasionally shower them with cash.

But even her report on urban affairs is uncharacteristically woolly. She doesn’t show that the great American city is on its last legs. The burg Jacobs focuses upon, Toronto, may be on the cusp of a renaissance or it may be dying. Both views are plausible: Jacobs notes the against-expectations growth of Toronto’s job market of late, while lamenting its inability to keep its streets clean. The words of the prophets may, indeed, be written on the subway walls, but Jacobs doesn’t make sense of them this time out.