One of the most significant disputes in early modern philosophy was between the moral rationalists and the moral sentimentalists. The moral rationalists – such as Ralph Cudworth, Samuel Clarke, and John Balguy – held that morality originated in reason alone. The moral sentimentalists – such as Anthony Ashley Cooper, the third Earl of Shaftesbury, Francis Hutcheson, and David Hume – held that morality originated at least partly in sentiment. In addition to other arguments, the rationalists and sentimentalists developed rich analogies. The most significant analogy the rationalists developed was between morality and mathematics. The most significant analogy the sentimentalists developed was between morality and beauty. These two analogies illustrate well the main ideas, underlying insights, and accounts of moral phenomenology the two positions have to offer. An examination of the two analogies will thus serve as a useful introduction to the debate between moral rationalism and moral sentimentalism as a whole.