[1] In standard Italian, syntactic doubling occurs after the following words (with exceptions described below): Articles, clitic pronouns (mi, ti, lo, etc.)
Phonetic results such as occasional /il kane/ → [i‿kˈkaːne] 'the dog' in colloquial (typically Tuscan) speech are transparent cases of synchronic assimilation.
[1] In some phonemic transcriptions, such as in the Zingarelli dictionary, words that trigger syntactic gemination are marked with an asterisk: e.g. the preposition "a" is transcribed as /a*/.
In northern Italy, San Marino and Switzerland speakers use it inconsistently because the feature is not present in the dialectal substratum, and it is not usually shown in the written language unless a single word is produced by the fusion of two constituent words: "chi sa"-> chissà ('who knows' in the sense of 'goodness knows').
It is not normally taught in the grammar programmes of Italian schools so most speakers are not consciously aware of its existence.
[2][citation needed] It does not occur in the following cases: There are other considerations, especially in various dialects, so that initial gemination is subject to complicated lexical, syntactic and phonological/prosodic conditions.