Jurisprudence is generally thought to consist of two main classical rival branches — natural law and legal positivism — followed by a bunch of modern schools — legal realism, law and economics, critical theory, legal pragmatism, etc. In this essay I argue that three main branches of jurisprudence have existed, and battled, for centuries, not two, but the third goes unrecognized as such because it has traveled under different labels and the underlying connections have been clouded by various confusions. The core insights and focus of this third branch, what I call “Social Legal Theory,” trace in a continuous thread from Montesquieu, through historical jurisprudence, sociological jurisprudence, and legal realism, up to the present. This third branch, I argue, provides a contrasting/complementary perspective, in conjunction with natural law and legal positivism, which rounds out the full range of theoretical angles on law: natural law is normative; legal positivism is analytical/conceptual; and social legal theory is empirical. (Among a number of clarifications, I answer the common objection that empirically-grounded theories are not sufficiently theoretical.) The conventional jurisprudential narrative is redrawn in this essay in a way that exposes unseen connections among theoretical schools and brings into focus critical issues about the nature of law that currently are marginalized by natural law and legal positivism.