Specifying truth-conditions

Sense relations can be established by specifying the truth-conditions of well-formed sentences in which lexemes occur. In the case of entailment, an implicational relationship implies in that if X is true, then Y must be true also, but the reverse relationship does not hold (i.e. if Y is true, then X need not be).

Another kind of sense relationship is synonymy, which involves identity of lexical meaning. Semanticists would argue that total synonymy is rare, if indeed it occurs at all in language. Hide and conceal, for example, might appear to be synonyms, because of their substitutability in a wide range of contexts, e.g.:

1 Was Saddam hiding/concealing weapons of mass destruction?

2 He’s been hiding/concealing the truth for some time.

3 They hide/conceal their secrets very well.

4 Finally he found the stolen necklace, hidden/concealed in an old musical box.

But the interchangeability is not total: conceal can’t be used, for example, as an intransitive verb (the kids are hiding/*concealing in the understairs cupboard), and no child ever asks to play conceal and seek.

Occasionally, two words with a technical meaning may be described as fully synonymous (tetanus and lockjaw, for example) but, even here, one form is likely to have different connotations from the other (lockjaw is a lower register, i.e. more informal, term than tetanus in this example), and it is a sign of efficiency within language systems that where two lexemes fulfil exactly the same role one will tend to oust the other. Perhaps for this reason lockjaw is an old-fashioned term these days, the medical term tetanus having largely prevailed in everyday usage.

Partial synonymy, on the other hand – as demonstrated by conceal and hide above, which overlap in many of their senses – is quite common: in some cases, different lexemes of similar or identical meaning are associated with different registers. While child might be preferred to kid except in informal situations, the more elevated term minor (or youth) might be appropriate in a formal or legal context.