Consider the development of so-called downtoners – grammatical elements that minimize the force of the word they accompany. Nineteenth-century English saw the emergence of a new downtoner, all but, meaning 'almost'. All but started out being used only with adjectives, as in her escape was all but miraculous. But later it also began to turn up with verbs, as in until his clothes all but dropped from him. In grammatical terms, that is a fairly big leap, but when looked at closely the leap is found to go in smaller steps. Before all but spread to verbs, it appeared with past participles, which very much resemble both adjectives and verbs, as in her breath was all but gone. So, changes can sneak into a language and spread from context to context by exploiting the similarities between contexts.
The role of similarity in language change makes a number of predictions. For one thing, actualization processes will differ from item to item because in each case there will be different similarities to exploit. English is currently seeing some nouns developing into adjectives, such as fun or key. This again goes by small adjustments, but along different pathways. For fun, speakers started from expressions like that was really fun, which they would adjust to that was very fun, and from there they would go on to a very fun time and by now some have even gone on to expressions like the funnest time ever. For key, change started from expressions like a key player, which could be adjusted to an absolutely key player, and from there to a player who is absolutely key. When the changes are over, the eventual outcome will be the same – fun and key will have all the characteristics of any other English adjective – but the way that is coming about is different.
Another prediction is that actualization processes will differ from language to language, because grammatical contexts that are similar in one language may not be in another. Comparing the development of another English downtoner, far from (as in far from perfect), to its Dutch equivalent, verre van, it is found that, even though they started out quite similar, the two downtoners went on to develop differently due to differences in the overall structure of English and Dutch. Importantly, this is one way in which even small changes may reinforce and gradually increase existing differences between languages.
Finally, this research can say something about how language works in general. Similarity is so important to how changes unfold precisely because it is important to how speakers subconsciously use language all the time. Presumably, whenever a speaker thinks up a new sentence and decides it is acceptable, they do so by evaluating its resemblance to previous sentences. In this respect, actualization processes are giving us a unique window on how similarity works in organizing and reorganizing speakers' internal grammars, showing just how sensitive speakers are to all sorts of similarities. Strikingly, then, the same similarity judgments that speakers make to form acceptable and intelligible sentences allow their grammars to gradually change over time.
EurekAlert. 2012. “How language change sneaks in”. EurekAlert. Posted: September 4, 2012. Available online: http://www.eurekalert.org/pub_releases/2012-09/lsoa-hlc083012.php