A friend of mine asked me the other day to explain the difference between I used to run every morning and I am used to running every morning. She understood, of course, the different meaning each had, but she wanted to know how the grammatical structure changed in order to change the meaning so clearly. The question of structure always involves thinking, so how could her question not be interesting?
Let’s begin by reminding ourselves that a thought, as opposed to a suggestion, is expressed in language by a clause. A clause, in turn, has two parts, a subject and a predicate, the subject naming what we want to say something about, and the predicate, with its verb, saying what we want to say about its subject. Every clause expresses a thought, and a sentence will therefore have as many thoughts as it has clauses. We should remember, too, that a thought in natural language is to be distinguished from a proposition in the technical language of logic, but let’s leave that for another day.
When we speak of the verb of a predicate, we properly mean what is termed a finite verb, because there may very well be another verb (as there is in each example) which is completing the meaning of the finite verb but not actually making a predication itself. A finite verb is so called because it is specific (that is, finite) as to the person, number, and tense of the subject. Another verb in the same clause and depending on that finite verb is called an infinitive. A finite verb actuates the meaning we comprehend in a clause, and an infinitive, if there is one, will round out the meaning of that thought.
If we look now at the predicates of the example sentences, we see that the finite verb of the first is used, and the finite verb of the second is am; the singular subject I remains the same for both. The transitive verb to use originally meant to accustom or habituate oneself to something, and when we now employ it with an infinitive, it conveys the idea of customary, ongoing past action: I used to run every morning means, more fulsomely, I once accustomed myself to running every morning. Some languages (Latin, French, and German among them) have what is termed an imperfect tense, whose special role is to describe this habitual past action, that is, action which is deliberately not being portrayed as complete, or in grammatical terms perfect. English regularly translates this tense it does not have in its standard six-tense scheme with the used + infinitive construction.
In the second example, however, something related but grammatically quite distinct is underway. To say I am used to running every morning is to assert a present state of being with the verb to be (am), and to identify the subject with an adjective in the predicate, used. If we remember the original definition of the verb use, the meaning becomes clear quickly: I am accustomed to running every morning. The word running here is a gerund (a noun built from a verb), and the preposition to shows, as it often does, the object, or destination we might say, of a quality named by an adjective: what it is I am accustomed to is running every morning.
Notice, importantly, that the tense of the finite verb of the first sentence is simple past, and that of the second is simple present. We can certainly change the latter to a simple past should the facts warrant it (I was accustomed to running every morning), but the verb used must be in the simple past (and only the simple past) in the special construction of used + infinitive to indicate ongoing past action. One last point to remember: the construction is used to, not use to. The latter is not Standard English.
And just what is Standard English? Let’s leave that for another day, too.
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