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Is there a difference between

I didn't use to do that

and

I used to not to do that

For example,

I don't use to read books when I was a child.

Would both be correct? Is the second even correct grammatically?

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marked as duplicate by RegDwigнt Oct 4 '13 at 13:41

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The idiom used to, always pronounced /'yustə/, can either be a verb in the past tense, followed by an infinitive, and presupposing that the present tense is false (I used to live on DeKalb Avenue); or preceded by a form of be, it means 'accustomed to; adapted to', as in I'm used to living on DeKalb Avenue now. –  John Lawler Oct 4 '13 at 4:41
    
I didn't used to read books, but now I do. –  Jim Oct 4 '13 at 5:00
1  
"I used to do a lot of drugs. I still do, but I used to, too." - Mitch Hedberg (re presupposition) –  hunter2 Oct 4 '13 at 6:20
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2 Answers

up vote 2 down vote accepted

According to Michael Swan's "Practical English Usage", the negative forms of used to are:

formal: used not to

informal: didn't use to, didn't used to

Example:

I didn't use(d) to read books when I was a child. (informal)

I used not to read books when I was a child. (formal)

So, the difference would be mostly that of register.

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I've never heard a native English speaker says I used not to do that or I used not to read books. How would it be pronounced, for starts? /ayustnat/ or /ayuzdnat/? Does Swan cover the pronunciation? If not, it's useless pedantry. –  John Lawler Oct 4 '13 at 16:15
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The first example suggests your habit, whereas your second example is not grammatically correct. Instead it should be "I used to not do that".

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