Having joined the officer training corps whist still at Rugby, on the outbreak of World War II, he volunteered to serve with the Royal Artillery.

His earliest work in philosophy, which has never been published, dates from this period, and in it,[8][9][10] he tried to develop a system that might "serve as a guide to life in the harshest conditions", according to C. C. W.

He left Oxford in 1983 to become Graduate Research Professor of Philosophy at the University of Florida at Gainesville, a post he held until 1994.

His book Sorting Out Ethics might be interpreted as saying that Hare is as much a Kantian as he is a utilitarian, but other sources[14] disagree with this assessment.

By the former, he meant that moral judgments must identify the situation they describe according to a finite set of universal terms, excluding proper names, but not definite descriptions.

This was identified by Frankena, Nobis and others as a major flaw in Hare's system, as it appeared to take no account of akrasia, or weakness of the will.

Hare departs from Kant's view that only the most general maxims of conduct be used (for example, "do not steal"), but the consequences ignored, when applying the categorical imperative.

To ignore consequences leads to absurdity: for example, that it would be wrong to steal a terrorist's plans to blow up a nuclear facility.

While Hare was primarily interested in meta-ethics, he also made some important contributions to the fields of political philosophy and applied ethics.