Tom Regan (/ˈreɪɡən/;[1] November 28, 1938 – February 17, 2017) was an American philosopher who specialized in animal rights theory.

Regan points out that we routinely ascribe inherent value, and thus the right to be treated with respect, to humans who are not rational, including infants and the severely mentally impaired.

[10] Supporters argue that Regan's argument for animal rights does not rely on a radical new theory of ethics, but that it follows from a consistent application of moral principles and insights that many of us already hold with respect to the ethical treatment of human beings; however, others criticize the lack of certainty with which Regan's "inherent value" or "subject-of-a-life" status can be determined, and note that the sufficient conditions he lists—for example, having sense-perceptions, beliefs, desires, motives, and memory—in effect reduce to "similarity to humans".

We have no basic right not to be harmed by those natural diseases we are heir to.” In the 1980s, Regan published three books on G. E. Moore's philosophy.

Using these materials, Regan argues that Principia's primary purpose was (as Moore wrote) to "humble the Science of Ethics" by exposing the "lies" told by "would-be scientific ethicists" ("Art, Morals, and Religion": May 5, 1901).

In Moore's view, a truly scientific ethic is able to prove very little concerning values, rules, duty, and virtues.

Not even all the rules commended by Common Sense qualify: only "most of those most universally recognized by Common Sense" are possible candidates, and even in their case Moore maintains only that the requisite type of justification "may be possible" (p. xxii, italics in the original).

In all cases of this sort, individuals should guide their choice "by a direct consideration of the effects which the action may produce" (p. XX), doing what one thinks will promote one' s own interests, as these are enlarged by the lives of others in whom one has "a strong personal interest" (Ibid., XX) instead of attempting to satisfy the demands of "a more extended beneficence," as in "the greatest good for the greatest number."

In short, in virtually all our activities in our day-to-day life we are at liberty to live and choose without troubling ourselves about whether we are doing what duty, in the form of the rules of morality, requires.

"Regan's thesis is that an adequate understanding of Moore's ethical philosophy can be achieved only when seen against the backdrop of Bloomsbury—the avant-garde group of free spirits (among whom were Lytton Strachey, Virginia Woolf, and John Maynard Keynes) who met weekly in London between 1905 and 1920.

Written with the verve appropriate to its subject, and yet philosophically scrupulous, this book deserves a place in philosophy and cultural history collections in both public and academic libraries."

[12] The Special Collections Research Center at NC State University set up an annual fellowship in memory of Regan.