Languages change continuously: the changes occur in phonetics, phonology, morphology, syntax, lexicon and semantics. Over time, a treasure trove of new words is created, but also another one containing lost words or, in any case, words with a more or less altered meaning. It also includes forms that have disappeared from use, but which have maintained their vitality for centuries. In this paper, we have considered a category of syncategorematic or grammatical words - conjunctions: their form is often conditioned not only by the function performed but also by the sequence in which they are placed. Their diachronic changes, both in form and function, therefore depend on the syntax, which sometimes modifies their phonetic structure and sometimes their grammatical value. Their changes have a different or perhaps broader influence, because they affect not only the changes in the lexical repertoire, but also in syntactic structures. Analyzing Italian conjunctions in this diachronic light, we found four groups of phenomena that led to the disappearance of variants, forms or meanings: changes in the lexical list of conjunctions and the disappearance of phono-orthographic variants replaced by one form with the result of homologation of the system in contemporary Italian; changes in the semantics of some conjunctions (some forms survive at the lexical level, but with the meaning changed); the disappearance of forms in the contemporary language (where the form survives only in literary use or in certain formal registers) and the definitive disappearance of forms. From the analyzes, it emerges that the disappearances that occurred in the category of conjunctions reflect a general tendency towards a shrinking of the system, to the reduction of the number of forms with the elimination of numerous phonoorthographic variants (which also occurred in other grammatical categories) but also with the fall into disuse of very vital lexical units in the Middle Ages. The analysis of the sample shows that some types of conjunctions, particularly concessive, causal and temporal ones, had a "superabundance" of forms that were eliminated over time, felt increasingly archaic starting from the sixteenth century and fell into disuse entirely in the nineteenth century. The most significant and emblematic example are probably concessive conjunctions. In the first prose in ancient Italian the number of units (and their frequency of use) was rather scarce (for example, in the Novellino we have identified only six concessive conjunctions: ancorché, avvegna che, benché, quanto che, quantunque and (con) tutto che). With the great authors of the fourteenth century, the system was enriched both in the variety of units and in the frequency to such an extent that in the Decameron we recorded 23 different concessive conjunctions (ancorché, avvegna che, benché, che che, come che, donde che, dove che, dovunque, eziandio se, malgrado, nonché, nonostante che, onde che, ove che, perché, per quanto, posto che, quando pur, quanto che, quantunque , sebbene, se pure and (con) tutto che). Today, however, only 14 are fully active. A similar situation also occurs in the other types of conjunctions. According to what has been shown, the shrinking process is still ongoing and we could expect other reductions in the number of units in use which today are beginning to prove archaic (allorché, allorquando, ancorché, appena che, checché, conforme che, donde, quasiché).