When several things agree in more than one quality, there may be an abstract term denoting the union of qualities in which they agree, and omitting their peculiarities; as 'human nature' denotes the common qualities of men, 'civilisation' the common conditions of civilised peoples.
Every general name, if used as a concrete term, has, or may have, a corresponding abstract term.

Sometimes the concrete term is modified to form the abstract, as 'greedy--greediness'; sometimes a word is adapted from another language, as 'man--humanity'; sometimes a composite term is used, as 'mercury--the nature of mercury,' etc.

The same concrete may have several abstract correlatives, as 'man--manhood, humanity, human nature'; 'heavy--weight, gravity, ponderosity'; but in such cases the abstract terms are not used quite synonymously; that is, they imply different ways of considering the concrete.
Whether a word is used as a concrete or abstract term is in most instances plain from the word itself, the use of most words being pretty regular one way or the other; but sometimes we must judge by the context.

'Weight' may be used in the abstract for 'gravity,' or in the concrete for a measure; but in the latter sense it is syncategorematic (in the singular), needing at least the article 'a (or the) weight.' 'Government' may mean 'supreme political authority,' and is then abstract; or, the men who happen to be ministers, and is then concrete; but in this case, too, the article is usually prefixed.

'The life' of any man may mean his vitality (abstract), as in "Thus following life in creatures we dissect"; or, the series of events through which he passes (concrete), as in 'the life of Nelson as narrated by Southey.' It has been made a question whether the denotation of an abstract term may itself be the subject of qualities.