In the 1860s and 1870s Herbert Spencer was the foremost living English philosopher. But he was so speculative that by 1880 in England his works rivaled those of Charles Darwin or John Stuart Mill only among libertarians and readers astonished by his ingenious scientism. His syntheses in a number of fields--political philosophy, education, metaphysics, biology, sociology, and ethics--were reductive, importing categories from biology into the human sciences. Since 1915 the post-Spencerian social sciences have separated from the natural sciences on the grounds that culture and its medium, language, are irreducible categories.

In the third quarter of his century, Spencer was a giant. To the century-old English ideology of uniform, self-acting laws of nature-Adam Smith's law of supply and demand, Thomas Malthus's law of population, and Jeremy Bentham's Utilitarian law of the natural identity of interests in society-he contributed a law of equals. He relied on a widely credited cause of...