" ‘Concrete reality’ contrasts with ‘abstract reality’: some hold that numbers and concepts are real things, part of reality, but are abstract entities rather than concrete entities. One quick way to characterize concrete reality is to say that to be concretely real is to be capable of entering into causal relations." That is Galen Strawson. Note the careful wording: this is a "quick way" of distinguishing concrete from abstract. Strawson is not presuming to offer it as a definition. This quote shows Strawson preparing to set out metaphysical views of his own, he is here speaking NOT in a history-of-philosophy context. But it brings to mind that, as my friend Henry has mentioned in comments on this blog, Strawson has set out a view of Humean notions of causation in which Hume's view is not what it has commonly been taken to be. Hume meant, Strawson says, only that our experience of causation is limited to correlation, not that the fact of ca...