I have found this sentence in javadoc for one class Thread. While I've understood its meaning, not sure if I understand its grammatical form.

Interrupting a thread that is not alive need not have any effect.

I could pull out "that is not alive" - quite clear. Then left

Interrupting a thread ... need not have any effect.

Looks like "a thread" could be also thrown away

Interrupting ... need not have any effect.

Is "need not + bare infinitive" a correct grammatical form?


3 Answers 3


...that is not alive...

This can be rephrased as inactive. Interrupting an inactive thread is no big deal. If you pull that out phrase out, and assume the rest is fine, then you are stating that any thread can be interrupted. If you take this route, you are setting a bad precedent.

Is "need not + infinitive" a correct grammatical form?

The infinitive, of course, is the word to used with the base form of a verb.

  • to cause
  • to interrupt
  • to read

How do the following read to you:

  • You need not to cause a problem.
  • Young children need not to interrupt conversing adults.
  • When you watch the movie you need not to read the book.

All of these examples (albeit crude) would sound smoother using a bare infinitive (using the root verb with to removed.) If you want to look at the rule book, see: Modals.

  • bare infinitive, yes. I've forgot how it's named correctly.
    – St.Shadow
    Jan 16, 2016 at 10:16
  • Well, I've split the sentence to understand it's grammar (with loosing meaning, of course). It's like with "James while John had had had had had had had had had had had a better effect on the teacher"
    – St.Shadow
    Jan 16, 2016 at 10:21

Interrupting a thread that is not alive need not have any effect.

If you interrupt a thread,
specifically a thread which is not alive,
the interruption may have no effect.

IMO, "Interrupting a thread that is not alive..." can be considered as a gerund here - a verb participle phrase or clause which is carrying out the role of a noun.

It can be understood as equivalent in meaning to "The act of interrupting a thread (which is not alive)..."

"...need not have..." can be understood as "...will not necessarily have..." or as "...may not have..."

"need not" used in conjunction with a (suitably declined part of) a verb is grammatically correct. It's perfectly correct, although it is no longer used as commonly as it used to be.

Please note that is not an infinitive being used here ; there is a subject for the verb.

"To need not do" would be an infinitive form - and I myself have never encountered this construct in the infinitive.

  • Well, I wasn't clear enough. I have understood the meaning, I haven't understood the grammatical structure.
    – St.Shadow
    Jan 16, 2016 at 10:15

It essentially means, if you interrupt a thread which is not alive, it may or may not have any effect (2 outcomes). In this sentence, it is framed as, "it need not have" which means "it doesn't necessarily have any effect"

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