 Other notable publications of Aaron's include an essay, "Two Senses of the Word Universal" (published in "Mind" in 1939) and "Our Knowledge of Universals", a study read to the British Academy in 1945 and published in volume 23 of its "Proceedings".Aaron's work shows fascination with the idea of a Universal, which culminated in a 1952 book "The Theory of Universals".Here he attacks the notion of universals as Platonic forms, but is equally critical of Aristotelian realism about essences, as he is of nominalism and conceptualism as theories of universals.