Which phrase is more suitable to convey one's inability to do something — "not able to" or "unable to"? For example,

  • not able to join the meeting
  • unable to join the meeting
  • 4
    Either, both seem natural to me as a native speaker, though I may lean slightly towards "unable" – James Webster Sep 27 '13 at 8:58
  • 1
    For example: I'm not able to come to a conclusion as to which is better since I am unable to decide which I use more often. – James Webster Sep 27 '13 at 9:00
  • To my ears, unable is more fitting for short-lived circumstances. I'm unable to answer the phone right now. I'm not able to come to the party on Friday. Nah, after I think about it, it sounds about the same. Actually, if I think about it some more, it's not quite the same. – Talia Ford Sep 27 '13 at 10:49
  • As a non-native English speaker, not able really throws me off, and I was quite surprised when I started moderating stackoverflow.com and found out that (seemingly) native English speakers tend to use not able rather than unable. – jojman Feb 3 '15 at 13:34

I interpret the sentences in different ways.

"He was unable to join the meeting" I read as, "he" was unable to join the meeting because of scheduling conflicts, or for reasons that made him decline participation in advance.

While I read "He was not able to join the meeting" as, "he" got held up in traffic or some other unforeseen situation prevented him from joining the meeting as he had planned.

I'm not sure there's any formal validity to this.

  • 4
    I’d say this is an optional distinction, one that can be made, but must not necessarily be made. If it is made, however, I agree with the distribution you describe. If I have no specific context, I would not necessarily infer scheduling conflicts or traffic jams from either version; but if I have a scheduling conflict, I would be more likely to say ‘I’m unable’, and if I’m stuck in traffic, I’d be more likely to say ‘I’m not able’ (or even more likely, ‘I won’t be able’). – Janus Bahs Jacquet Sep 27 '13 at 12:10
  • One is "I could but won't bc my priorities are different", the other signifies literal impossibility. – Nearoo Jul 30 at 12:58

I think, 'Unable' denotes internal cause or inability and 'not able' external constraints.

  • 4
    Hello, Praveen. Have you any authoritative support for this view? It's not a distinction I'm familiar with. – Edwin Ashworth Jul 20 '15 at 16:10

I try to think of it as unsuccessful vs. not successful. "Not successful" is more general, whereas "unsuccessful" implies there is a set goal that was not accomplished. Or is it unaccomplished? And I'm not really sure how this applies to "able". Maybe I should take more English courses...


I'm not able to attend the meeting. Here it implies some or other reason is the cause.I am unable to lift 100kg. It is purely inability of the person.

  • Why do you think this? I don't think that "not able" means the cause is external... – curiousdannii Jul 21 '14 at 11:45

Not able :not of permanent nature. Unable :most likely of permanent nature.

  • 4
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  • What evidence do you have for these meanings? I don't think they are correct. – curiousdannii Jul 21 '14 at 11:45

protected by user140086 May 31 '16 at 15:38

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