"Because it’s there": climber George Mallory’s poetic motivation to climb Everest at risk to his life may appear anything but logical. Yet to an economist, Mallory was probably rational; costs and benefits must have figured somewhere in his reasoning. Tim Harford’s new book explores both the delightful and odious outcomes of the economist’s assumption of human rationality. His contention that racism, addiction, divorce and the excesses of executive pay are all the products of rational action is at the same time compelling and distressing. The writing is engaging but his broad, populist definition of rationality renders some conclusions unsurprising, and an overall work that is, to paraphrase an excellent chapter, "spiky".

The book opens poorly, questioning the rationality of blow jobs, in a piece of calculated sensationalism that tries too hard. We are then dragged, via a Dickensian cast list of prostitutes, gamblers and academics, to his conclusion that there’s method in our apparent madness. The valid point is that non-monetary costs and benefits (like AIDS and sexual pleasure) provide incentives just as money does.

A chapter on divorce and relationships ‘proves’ that women are largely attracted to richer men, as though decades of evolutionary biology had not settled the issue. And male students who join ballroom dancing societies at universities could have told Harford that we respond to supply and demand when looking for a potential mate, rather than seek ‘the one’.

The book improves in later chapters as Harford discusses executive pay, discrimination and cities. For example, CEOs are paid like tennis stars, because firms want to reward performance; but because it’s difficult to observe the required behaviour, managers are interested in relative performance between staff. High pay therefore serves as an incentive to create motivation for staff in a ‘tournament’ in which people are assumed to be doing their utmost to win. The following chapter reveals how discrimination against workers blunts the incentives for those workers to get an education, increasing the success of the discrimination strategy – illustrating Harford’s point that rationality is something we should at least consider in all circumstances. The book peaks with an excellent discussion on cities explaining that people are willing to pay high city rents because they are an admission fee to a theme park of opportunities, chance meetings and luck that can enhance one’s career prospects. In an age when technology was once supposed to be killing geography, the importance of cities becomes more important because it makes those chance encounters more possible.

Not all the research is convincing and at times Harford creates artificial divisions between the social sciences to demonstrate the superiority of economic explanations. Some may find this imperialism grating: that anything affecting behaviour can be a cost or benefit means that all explanations are, in a trivial sense, economic. Yet that is also a profound insight. Knowing when economics adds real insight, though, is a function of the problem under the lens. John Kay has said that it’s mistaken to think there are ‘true’ explanations of social phenomena: we buy drinks in rounds both because it minimises transaction costs (economic) and because it fosters kinship (anthropological). The Logic of Life’s assumption is that economics trumps other explanations because it offers the best cures for society’s ills. You may not be convinced but you’d be wrong to discount it entirely.