To an economist or a journalist who is used to thinking of a decade as long enough for entire theories to rise and fall, an age is the longest period imaginable; durable ideas can be age-old and this age is synonymous with 'this world' or 'everything'.

Can anyone explain why thinking, and not think is used in that passage?

Would it be ungrammatical replacing thinking with think?

Or, otherwise, that replacing would be grammatical but it would produce a change in meaning. If so, can anyone explain what this change in meaning is?

  • 2
    Again, be used to [noun phrase] is an idiom. Here, the NP contains a gerund, the form of a verb that functions like a noun. The to in this idiom is not an infinitive marker, so it can't be followed by an infinitive verb.
    – user230
    Dec 7, 2013 at 12:41

2 Answers 2


A good trick to avoid such confusion is to remember that there are two different entries used to in a dictionary. The typical usages are:

  • used [infinitive] is for habits in the past. Here, used to is a verb, e.g., I used to play badminton.
  • used to [verb-ing] (also used to [noun]) is for familiarity. Here used to is an adjective, and you always need verb to be in front of it, e.g., I've lived in Central London for six years now, so I'm used to driving in London now. I'm used to the noise too.

Compare these two sentences:

I am used to playing badminton.
I used to play badminton.

The first (I am used to playing) means: I have played badminton often enough, so you can expect me to know what badminton is and to play it well enough. The second (I used to play) means: I played badminton regularly for a certain amount of time in the past. (I don't play it anymore.)

In your question, it would be ungrammatical if you replaced thinking with think. Do not write "He is used to think ...". Always write "He is used to thinking ..." to mean that he is familiar with that kind of thinking. However, if you want to mean that he changed his opinion, use "He used to think ...". For example, "He used to think smoking is good."


for more information, I would like to post some differences of some similar forms of used to.

  1. [used to + general verb] means habitual actions in the past but now he or she doesn't do this.

  2. [be used to N/-ing] is also used as [be accustomed to N/-ing]

  3. [be used to + general verb] is passive form and if you use for instead of to, you can put the reason or purpose at the end of this expression.

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