My topic is equality: the proposition that humans are all one another's equals – created equal, perhaps, or (whether created or not) just equal, in some fundamental and compelling sense. What that sense is and what its implications are for law, politics, society, and economy – these are questions I propose to explore in the company of the seventeenth-century English political philosopher John Locke.

I believe that Locke's mature corpus – An Essay Concerning Human Understanding, the Two Treatises of Government, the four (or rather three-and-a-half) Letters Concerning Toleration that he wrote in the 1680s and 1690s, and The Reasonableness of Christianity – is as well-worked-out a theory of basic equality as we have in the canon of political philosophy. I shall not try to defend that proposition in this introductory chapter; the whole book may be read as a defense of it. But I want to say something preliminary here, first about what I mean by “basic equality” and, secondly, about my use of political, philosophical, and religious writings from the 1680s and the 1690s in relation to our largely secular interest in this topic at the beginning of the twenty-first century.

First, a word about basic equality. In the voluminous modern literature on egalitarianism, there is a tremendous amount on equality as a policy aim. Philosophers ask whether we should be aiming for equality of wealth, equality of income, equality of happiness, or equality of opportunity; they ask whether equality is an acceptable aim in itself or code for something else, like the mitigation of poverty; they ask whether aiming for equality implies an unacceptable leveling; whether, if achieved, it could possibly be stable; how it is related to other social values such as efficiency, liberty, and the rule of law; and so on.