The Merriam-Webster Dictionary defines presentism generally, as "an attitude toward the past dominated by present-day attitudes and experiences." In historiography, it is used more narrowly, to judge ethical behavior or terminology based on modern usage, rather than the usage familiar to the subjects of the discussion.
It is a measure of the change that has occurred in the past thirty years that the one thing Jefferson's children nowadays are most likely to associate with him, apart from his authorship of the Declaration of Independence, is a sexual liaison with one of his slaves, Sally Hemings. College teachers are often dismayed to discover that many if not most of their students now regard this as an accepted fact. But this is not all. In the prevailing ethos of the sexual revolution, Jefferson's supposed liaison is widely received with equanimity and seems to earn him nothing more reproachful than a knowing smile.