There are three causes of ignorance for Locke which he identifies in IV, III, XX of the Essay. Locke identifies ‘ignorance’ with “the dark side” of our knowledge, which is “infinitely larger than our knowledge” (IV, III, XX). The causes of ignorance are as follows: (i) Want of ideas, (ii) want of a discoverable connexion between the ideas we have and (iii) want of tracing and examining our ideas. Regarding (i), Locke writes that “how much these few and narrow inlets [i.e., lack quantitatively of ideas we have] are disproportionate to the vast whole extent of all beings” (IV, III, XXIII). Part of our cognitive situation, says Locke, is the inability to plunder the quantity of ideas which are to be had, though which we cannot fathom to attain. For example, in wondering whether abortion is ever morally permissible, one might consult the virtually endless list of ethical theories. Either one can find a plausible theory which matches our moral experience, or one can suggest that the moral disagreement is constitutive of a reason to deny the meaningfulness of the question (or be skeptical to an answer at all). However, how do we move from a quantity of ideas to skepticism? We do not do this in the realm of ethical theory generally (nor in daily life). For example, suppose one asks: Is there something wrong with a psychopathic maniac who brings an automatic weapon into an elementary school and takes the lives of children and teachers? Of course, our answer is yes. However, there are theories in which this may have been utility-conducive (utilitarianism), appropriate given the right consequences (consequentialism) or perhaps even a meaningless question altogether (moral anti-realism). However, the sheer amount of theories does not diminish the wrongfulness of the action and our knowing that it is wrong. If we are consistent, the same applies to the moral status of the preborn i.e., sheer amounts of theories do not make the question “too difficult to answer” nor “meaningless.” Second, (ii) states that there is a de facto skepticism regarding the connection between many of the ideas of experience. Locke says: “How any thought should produce a motion in body is as remote from the nature of our ideas, as how any body should produce any thought in the mind” (IV, III, XVIII). To take the former as exemplary, we know that thoughts produce motions in our bodies i.e., anxious thoughts cause the heart rate to increase, though we have no idea as to the mechanical ‘how’—the connection—between the two. However, Locke’s second form of ignorance can be extrapolated into thinking about our moral intuitions regarding abortion. For example, one might think that a preborn human being is a collection of cells (or unicellular, if zygotic) and therefore unworthy of a moral status; however, in seeing a post-abortive operation, one might be convinced that there is something wrong with destroying the life of the preborn. It is this lack of putting beliefs together which results in ignorance (and also cognitive dissonance). Finally, (iii) claims that we are often ignorant not in virtue of the uncertainty of the object of inquiry nor in virtue of our cognitive capacities; rather, we are ignorant “for want of application in acquiring, examining, and by due ways comparing those ideas.” (IV, III, XXX). For example, if the preborn are—as we have good reason to believe—living, growing human beings, and we also accept that all human beings have human rights (including the right to life), it follows that abortion is a human rights violation. It is only in our ignorance that we do not put the two beliefs together, and consistently accept the conclusion.
 Although unlike Locke—and much of the Western philosophical tradition—I do not see a problem with thought/body (soul/body) interaction. See Rashad Rehman “Disintegrating Particles, Non-Local Causation and Category Mistakes: What do Conservation Laws have to do with Dualism?” Conatus Journal of Philosophy (accepted for the 3rd volume, 2018).