Moon elaborates the defining criteria with three specific properties inherent in each idiom, combined called their 'idiomaticity': 'institutionalization' (synonymous to some with 'lexicalization'); 'lexicogrammatical fixedness' (also termed 'frozenness'); and 'non-compositionality'
(unmotivatedness, or unanalyzability or opacity).
Typical of institutionalization (lexicalization) is that potential ambiguity is irrelevant, while only some,
potentially only one, from among all the possible
interpretations are meant (Bauer 1983,4). No qualities of a lexical string make one interpretation excel the others as
such, it is only its familiarity to the person in question that he or she associates it with a certain meaning.
Or as Bauer says: "There is nothing in the form
telephone box to prevent it from meaning a box shaped like a telephone, or a box which is located at a telephone, and so on; it is only because it is known to be synonymous with
telephone kiosk" (1983,48). In Meys's (1975) terms: telephone box has been transferred from being type familiar to being item familiar: it is not just the construction, which is recognized, but the particular lexeme (cited in Bauer 1983,48). In other words, the string has been
institutionalized. As stated, to some scholars this process is synonymous with that of lexicalization. Others, for
example Quirk et al. (1985,152) and Lipka (1990,95), make a distinction between the two.
To Lipka, in the process of lexicalization "a complex lexeme once coined tends to become a single complete lexical unit, a simple lexeme", while in the question of
institutionalization, both he and Quirk et al. agree with the above view by Bauer in equating it with "integration of a lexical item, with a particular form and meaning, into the existing stock of words as a generally acceptable and current lexeme" (Lipka 1990,95-6). In other words, a complex lexeme is institutionalized when the original nonce-formation is accepted by other speakers as a known lexical item. In short, lexicalization is the last stage in the process of a
metaphorical term losing its compositionality (motivation), and, as a result, turning into an idiom.
Lexicogrammatical fixedness, formal rigidity, refers to fixed expressions where only certain form or order of the constituents is possible. To describe the frozenness of the typical idiom, the compilers of LongId present (p.viii) three crucial operations that distinguish idiomatic phrases from normal ones, which they call literal phrases.
First, it is often impossible to substitute elements of the former with a semantically related word; for instance
"the man gave up the apparition" has lost the idiomatic reading of somebody dying implied by "the man gave up the ghost", and the same is true for the variant "the man
released the ghost". Secondly, in a literal phrase a noun may be substituted with a pronoun, but this is usually impossible in an idiom without the loss of the original, idiomatic
meaning. With such a substitution, for instance "he spilt the beans about my new job" becomes "he spilt them about my new job", losing the idiomatic reading of 'letting out a secret'.
Thirdly, passivization, which is normally operable (without a semantic loss) with transitive verbs, renders unnatural
readings for idiomatic phrases. This produces sentences like
"at three o'clock the ghost was given up by the man". In addition, some other grammatical operations normally viable with literal phrases may become impossible, as instanced by the pluralization in "the men gave up the ghosts".
As a rule, idiomatic phrases show great variety in terms of fixedness, whether lexical or grammatical, and the same is true of the whole phenomenon, i.e. the quality of a phrase of being idiomatic, or its idiomaticity. In other words,
idiomaticity is a quality of degree or scale. In addition to Bolinger (1977,168 as cited in Moon 1998,6), this view is shared by some other scholars, for instance Fernando and Flavell: "... idiomaticity is a phenomenon too complex to be defined in terms of a single property. Idiomaticity is best defined by multiple criteria, each criterion representing a single property” (1981,19 as cited in Moon 1998,6).
Like fixedness, also idiomaticity is a matter of degree.
In Moon's terms an idiomatic string may vary from the 'archetypal' form of semantic non-compositionality to
pragmatic, i.e. "the string is decodable compositionally, but the unit has a special discoursal function" (1998,8), as
instanced by proverbs, similes, and sayings. To describe the cases of incomplete non-compositionality, the term "compositional" is used by Moon to describe some
semi-idiomatic formulations adopted by primates as reported by Aitchison (1992,40ff. as cited in Moon 1998,6), such as
banana which is green 'cucumber', eye hat 'mask', and white tiger 'zebra'. These semi-compositional formulations
..."clearly show principles of analogy and motivation underlying attempts to overcome a restricted vocabulary"
(1998,6).
Similar intermediate status is shown by some common idiomatic phrases like spill the beans or rock the boat, which are partly compositional both structurally and
metaphorically in that "we can understand and appreciate the pertinence of the image" (1998,8). In other words, 'semi-idioms' have one component or more making them partly
motivated, or transparent. It is often stated that they have, accordingly, at least two readings, one or more literal and the idiomatic one, and are, as a result, used far more in their idiomatic than the literal sense (cf. LongId, p.viii).
Due to this double interpretation, some scholars have
suggested that even native speakers may be unaware of this ambiguity of metaphorical idioms, or, alternatively,
recognize them only as idioms. This view, shared among others by Cowie, Mackin & McCaig (OxfId, p.xiii), is contestable;
Van Lancker and Carter (1981) and Van Lancker et al. (1981), among others, show evidence from experiment-based results suggesting that native speakers are fully aware of these alternative interpretations and are even capable of
non-verbal communication as to what interpretation of the two is involved in each speech situation (in Moon 1998,9).
Another point worth noting and equally inherent in a typical idiom (as ambiguity) is their special tendency to present themselves in certain more or less fixed 'clots' or solidifications which tend to resist external changes. In this quality they gain some of the specific characteristics
of a word (lexeme). In Cruse's (1986,38) words: "Although idioms consist of more than one word they display to some extent the sort of internal cohesion that we expect of single words”. As stated earlier, they resist grammatical
modifications, such as interruption, insertion, and substitution or re-ordering of constituents.
To catch something of this idiom-specific feature of internal cohesion and external immunity, above compared with the clotting characteristic of blood, repeated attempts were made to arrive at a formula, sufficiently free and general to allow the enormous variety of such solidification, and
sufficiently concise to allow a short description. Various structural classifications delineated above, though clear-cut and illustrating the rich diversity of the English idiom, are therefore substituted by a fresh approach of description, presented in detail in Section V.3. One of the justifications of such a venture is the author's firm belief that such a novel view will allow some other scholars to make further use of it and be thus capable of describing this aspect of the idiom better than has been the case up to the present.