Last week Stanley John shared his pet linguistic peeve with me: the use of used to for the past imperfective repetitive. The imperfective aspect of verbs is a form of the verb that indicates either (a) continuing action (I was walking) or (b) repetitive action (I walked several times). The problem in English is that I walked is also the simple past, so English has no way of distinguishing walking once and walking multiple times in the past, present, or future tenses.
That is why, although we still spell it used to, we in fact pronounce this expression [usta] and it behaves like an auxiliary verb in a class with have, will, can. These are not regular verbs but “function words” that indicate various functions of the main verb. In Turkish and other languages their meaning is carried by suffixes: perfective aspect, future tense, etc. Usta has become the marker for the perfective repetitive (“iterative” in linguistic terms) aspect, a function which distinguishes action on the basis of whether it is completed or not.
Languages change for reasons that are not all clear. Markers of grammatical functions come and go. English among all other Indo-European languages has lost the distinction between singular and plural 2nd person pronouns; you is both singular and plural, polite and familiar. But we need that distinction so, as I’ve pointed out many times before, the phrase “you all” has been reduced to a plural pronoun, yall, all across the United States.
The same process accounts for usta: “I usta walk” makes it clear that the activity was habitual, repetitive, that it occurred more than once. With this auxiliary verb we can now distinguish between “I usta walk to work” without adding “every day” from “I walked to work” when we only mean “just this one time today”.
We might as well get used to (unreduced) it: when this kind of change sets into the vocabularies of millions of speakers, there is no turning back.