Accidental gap

In linguistics an accidental gap, also known as a gap, lexical gap, lacuna, or a hole in the pattern, is a word or other form that does not exist in some language but which would be permitted by the grammatical rules of the language. Accidental gaps differ from systematic gaps, those words or other forms which do not exist in a language due to the boundaries set by phonological, morphological, and other rules of that specific language.

In English, for example, a word pronounced /pfnk/ cannot exist because it has no vowels and therefore does not obey the word-formation rules of English. This is a systematic gap. In contrast, the string /peɪ̯k/ obeys English word-formation rules, but is not a word in English. Although theoretically such a word could exist, it does not; its absence is therefore an accidental gap. Such gaps are characteristic of idiom, the peculiar form of languages and language families.

Various types of accidental gaps exist. Phonological gaps are either words allowed by the phonological system of a language which do not actually exist, or sound contrasts missing from one paradigm of the phonological system itself. Morphological gaps are non-existent words predicted by the morphological system. A semantic gap refers to the non-existence of a word to describe a difference in meaning seen in other sets of words within the language.