 R. G. Collingwood (1889–1943) was primarily a philosopher of history, a metaphysican and archaeologist, and considered his work in aesthetics—the principal work being his The Principles of Art (1938)—as secondary (for more about his general philosophy, see the entry on  Robin George Collingwood).  But the work in aesthetics has enjoyed a persistent readership that continues into the present. In the years after WWII he was probably the most widely read and influential aesthetician to have written in English since Addison, Hutcheson and Hume (not counting Ruskin as an aesthetician), and to this day continues to make his way into anthologies as a principal proponent of the expressive theory of art. In the field of the philosophy of history, Collingwood famously held the doctrine of ‘Re-enactment’: since the subject is human beings in action, the historian cannot achieve understanding by describing what happened from an external point of view, but must elicit in the reader’s own mind the thoughts that were taking place in the principal actors involved in historical events. Similarly, the aesthetic procedure is one whereby the artist and spectator jointly come to realize, to come to know, certain mental states (see Guyer 2018). Art is fundamentally expression. Collingwood saw two main obstacles to general understanding and acceptance of this: First, the word ‘art’ has surreptitiously acquired multiple meanings among ordinary folk which should be disentangled; second, a philosophical theory of the phenomenon of expression is needed to show that it is an essential part of the life of the mind, not just a special activity that poets go in for. (Collingwood actually published an earlier theory of art in Outlines of a Philosophy of Art, but came to regard that theory as mistaken, superseded by the one in Principles of Art; what follows, and all references, concern the latter only).