In this three-paper dissertation, I examine three seemingly unconnected historical philosophers--Locke, Cockburn, and Kant--on questions concerning moral knowledge, human nature, and moral development. In the first chapter, my focus is on Locke's peculiar claim that a demonstrative science of morality is possible, and I address an interpretive problem in the literature according to which, for Locke, if moral knowledge is "certain" it would fail to be "instructive" because such knowledge would be vacuous. To ameliorate this bind, I offer my novel account of what certainty is for Locke, and I conclude that with a better understanding of certainty, we can see that moral knowledge is certain knowledge which fails to be instructive "not because it is vacuous" but because it is too general. In the second chapter, I offer my interpretation of morality-as-demonstrable as Cockburn weighs in on it. I argue that Cockburn offers a demonstration of the nature of moral obligation and that she offers a reflective method (grounded in human nature--with a focus on our "sociability") for demonstrating our particular moral duties. Thus, while Locke leaves moral knowledge too general, Cockburn get us closer to the level of more specific standards of action. Finally, in the third chapter, I examine a necessary (and necessarily "social") accompaniment to moral knowledge--moral development--as I offer my novel interpretation of "permissible moral illusions" in Kant. These communal practices, which help to awaken our fundamental moral considerations and foster attitudes of "love" and "respect" for our fellow human beings, get us yet closer to the ground than Cockburn. Accordingly, my reading offers insight into how we can become more sensitive to moral demands given our relatively imperfect moral knowledge. Thus, in each chapter, I address textual puzzles and offer novel views. Moreover, despite that each of these chapters can stand alone, what we find on a close examination of these three seemingly unconnected philosophers is that a rather rich conversation emerges between them in the developing picture of 17th and 18th century moral philosophy. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]