Syntactic gemination, or syntactic doubling, is an external sandhi phenomenon in Italian and some other Western Romance languages. It consists in the lengthening (gemination) of the initial consonant after words of certain categories.
The phenomenon is variously referred to in the English language as word-initial gemination, phonosyntactic consonantal gemination, as well as under the native Italian terms: raddoppiamento sintattico (RS), raddoppiamento fonosintattico (RF), raddoppiamento iniziale, rafforzamento iniziale (della consonante)
In standard Italian, syntactic doubling occurs after the following words (with exceptions described below):
- all stressed ("strong") monosyllables (monosillabi forti) and many unstressed ("weak") monosyllables: è, e, o, a, da, fra, che, se, ma, più, può, gru, gnu, re, blu, tre, ciò, sì, già, giù, là, lì, qua, qui, né, sci, tè
- Example: Andiamo a casa [anˈdjaːmo akˈkaːza], Let's go home
- all polysyllables stressed on the final vowel (this and the previous types are called oxytone words)
- Example: Parigi è una città bellissima [paˈriːd͡ʒi ɛ una t͡ʃitˈtabbelˈlissima], Paris is a very beautiful city
- some paroxytone words (stress on the second last syllable): come, dove, qualche, sopra (sovra)
- Example: Come va? [ˈkomevˈva], How are you?
The cases of doubling are commonly classified as "stress-induced doubling" and "lexical".
"Syntactic" means that gemination spans word boundaries, as opposed to the ordinary geminated consonants: "grappa". The emergence of syntactic doubling has traditionally been explained by a diachronic phenomenon of the loss of terminal consonants in Italian during its evolution from the Latin language (ad->a, quid->qui, etc.), but more recent research also pays attention to synchronic aspects.
Syntactic doubling is the standard native pronunciation in Tuscan, Central (both "stress-induced" and "lexical") and Southern Italy (only "lexical"), including Sicily and Corsica. In the Northern Italian versions of standard Italian, including Sardinia, speakers have difficulty using it correctly because the feature is not present in the dialectal substratum and is not usually shown in the written language unless a new word is produced by the fusion of the two: "chi sa"-> chissà ("who knows" in the sense goodness knows).
Syntactic doubling is not part of normal grammar programmes in Italian schools so most people who do not have a specific training in phonetics (such as the few people who studied linguistics or attended courses in theatrical pronunciation) typically do not recognize it as a standard feature of the language. Many Italian speakers are persuaded mistakenly that syntactic doubling is a pronunciation error typical of Central and Southern Italy. Thus, Northern speakers often do not even try to acquire the feature, and other speakers try to avoid it when speaking in formal situations.
Exceptions to the basic rules
Consonant gemination does not happen in the following cases:
- a pause occurs on the boundary of word in question
- In particular, the initial gemination may be conditioned by syntax, determining the likelihood of pause. For example, in the phrase "La volpe ne aveva mangiato metà prima di addormentarsi" ("The fox had eaten half of it before falling asleep"), there is no gemination after metà if there is even a slight pause, as prima is part of the adjunct, a sentence element easily isolated phonologically from the main clause within the prosodic hierarchy of the phrase.
- the stressed final vowel is lengthened 
- a sharp break or change in the pitch on the word boundary happens
There are other considerations, especially in various dialects, so the initial gemination is in fact subject to complicated lexical, syntactic, and phonological/prosodic conditions.
- Migliorini, Bruno; Tagliavini, Carlo; Fiorelli, Piero; Bórri, Tommaso Francesco (31 January 2008). "come". Dizionario d'ortografia e di pronunzia (DOP) (in Italian). Rai Eri. Retrieved 26 February 2010.
- Doris Borrelli (2002) "Raddoppiamento Sintattico in Italian: A Synchronic and Diachronic Cross-Dialectical Study" (Outstanding Dissertations in Linguistics) Routledge, ISBN 0-415-94207-1
- Absalom, Matthew, Stevens, Mary, and Hajek, John, "A Typology of Spreading, Insertion and Deletion or What You Weren’t Told About Raddoppiamento Sintattico in Italian", in "Proc. 2002 Conference of the Australian Linguistic Society", Macquarie University (e-print pdf file)
- Nespor, Marina & Irene Vogel (1986). Prosodic Phonology. Dordrecht: Foris.
- Syntactic Doubling
- Robert A. Hall, Jr. "Initial Consonants and Syntactic Doubling in West Romance", Language, Vol. 40, No. 4 (1964), pp. 551–556
- Loporcaro M, "L’origine del raddoppiamento fonosintattico: saggio di fonologia diacronica romanza", Francke Verlag, Basel, 1997.
- Absalom, Matthew, and Hajek, John (2006), "Raddoppiamento sintattico and Prosodic Phonology: A Re-evaluation" (also PDF), In Allan, Keith, Eds. Proceedings 2005 Conference of the Australian Linguistics Society, Monash University.