E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
are numbers considered abstractly1, 2, 3; but if we say 1 year, 2 feet, 3 men, etc., the numbers are no longer abstract, but concrete.
Taken in the abstract. Things are said to be taken in the abstract when they are considered absolutely, that is, without reference to other matters or persons. Thus, in the abstract, one man is as good as another, but not so socially and politically.