not able (unable)

Writers often ask: is 'not able' wrong? Use this compact reference to pick the clearest phrasing, with rewrite patterns and plenty of workplace, school, and casual examples you can copy or adapt.

Read the quick answer, then use the templates and example bank to fix sentences fast.

Quick answer

'Not able' is grammatically correct. 'Unable' is a one-word adjective with the same meaning and is usually cleaner and more formal. Use 'unable' for concise, formal writing; use 'not able', contractions, or alternatives (I can't, I won't be able, I'm afraid I can't) for conversation or a softer tone.

Formal/written: prefer 'unable' - "I am unable to attend."
Casual/spoken: "I'm not able" or "I can't" fits better - "Sorry, I can't tonight."
Future plans: "I won't be able" avoids ambiguity - "I won't be able to join next week."

Core explanation: short grammar check

'Unable' = un- (not) + able: a single adjective. 'Not able' = not + able: two words. Both mean the same thing and both are grammatical.

Both constructions are normally followed by an infinitive: 'unable to + verb' or 'not able to + verb'. Tone and brevity decide which to pick.

'Unable' - compact and formal: "She was unable to attend."
'Not able' - conversational and can emphasize the negation: "I'm not able to make it."
Always follow with 'to' + verb: incorrect - "unable attend"; correct - "unable to attend."

Real usage and tone: which to pick and why

'Unable' reads tighter on the page, so use it for reports, formal emails, and published text. 'Not able' or "I'm not able" sounds more natural in chat or when you want a softer refusal.

A softener (I'm afraid, unfortunately, sorry) often changes tone more than swapping 'unable' for 'not able'. For future events, prefer "I won't be able" to signal plans rather than present inability.

'Unable' = formal / direct / succinct.
'Not able' or "I can't" = casual / softer / conversational.
Use "I won't be able" for future commitments.

Fix your sentence: checklist and templates

Quick checklist: 1) Formal context? Use 'unable'. 2) Want softer tone? Use "I'm not able" or "I can't". 3) Talking about the future? Use "I won't be able". 4) Add a brief reason or next step when possible.

Formal present: "I am unable to [verb]." - e.g., "I am unable to attend."
Casual present: "I'm not able to [verb]" or "I can't [verb]." - e.g., "I'm not able to join."
Future: "I won't be able to [verb]." - e.g., "I won't be able to make the meeting on Monday."
Polite softeners: "I'm afraid," "Unfortunately," "Sorry -" before any choice.

Rewrite:
Original: "I am not able to attend the training." →
Formal: "I am unable to attend the training." →
Casual: "Sorry, I can't make the training."
Rewrite:
Original: "I am not able to come tomorrow." → "I'm afraid I can't come tomorrow."
Rewrite:
Original: "I am not able to meet the deadline." → "I am unable to meet the deadline; can we extend it to Friday?"

Examples: workplace, school, and casual - wrong/right pairs

Choose the version that matches your tone and add reasons or alternatives when appropriate.

Work
Wrong: "I am not able to finish the report by Friday." →
Right: "I am unable to finish the report by Friday. Can I deliver it Monday instead?"
Wrong: "We are not able to approve this request at this time." →
Right: "We are unable to approve this request at this time. Please resubmit with the missing documents."
Wrong: "I'm not able to join the client call tomorrow." →
Right: "I'm unable to join the client call tomorrow; can you share notes afterward?"
School
Wrong: "She was not able to submit her assignment before the deadline." →
Right: "She was unable to submit her assignment before the deadline and has requested an extension."
Wrong: "I am not able to solve problem 4 on the worksheet." →
Right: "I am unable to solve problem 4; could you explain step 2?"
Wrong: "They were not able to complete the lab due to equipment issues." →
Right: "They were unable to complete the lab due to equipment issues; we will reschedule."
Casual
Wrong: "Not able to join tonight, sorry." →
Right: "Sorry - I can't join tonight. Rain check?"
Wrong: "I am not able to go out - got too much work." →
Right: "I can't go out - swamped with work. Next weekend?"
Wrong: "I'm not able to help with that." →
Right: "I'm afraid I can't help with that right now - try asking Sam?"

Try your own sentence

Test the whole sentence in context. The surrounding words usually make the best phrasing obvious.

Quick swaps and extra rewrite patterns (copy/paste ready)

Short patterns to rewrite quickly; add a softener or a reason if needed.

Formal present: "I am unable to [verb]." → "I am unable to approve the request."
Casual present: "I can't [verb]." → "I can't make it tonight."
Future: "I won't be able to [verb]." → "I won't be able to join next week."
Polite alternative: "I'm afraid I can't [verb]." → "I'm afraid I can't attend the meeting."
Offer a next step: add "- can we reschedule?" or "- could you send the materials?"

Original: "I am not able to attend." →
Formal: "I am unable to attend."
Original: "I am not able to help today." →
Casual: "I can't help today, sorry."
Original: "I am not able to make it next week." → Future: "I won't be able to make it next week."
Original: "I am not able to access the file." → Polite + next step: "I am unable to access the file. Could you re-share it?"
Original: "We are not able to deliver on time." → "We are unable to deliver on time; expected delivery is Friday."

Hyphenation, spacing, and small style notes

'Unable' is one solid word. 'Not able' is two words. Never hyphenate either ('un-able', 'not-able' are wrong).

Use contractions in informal contexts: "I'm not able" is fine in chat; avoid contractions in formal documents. Always follow with 'to' + verb.

Correct: 'unable', 'not able', "I'm not able", 'cannot' (one word).
Incorrect: 'un able', 'un-able', 'not-able', 'can not' (unless you mean 'can' + 'not' for emphasis).
Follow with infinitive: 'unable to + verb' and 'not able to + verb'.

Memory trick and similar mistakes to watch for

Mnemonic: un + able = unable - the "squished" one-word form equals "not able." Use the squished form when you want compact, formal language.

Watch these nearby mistakes: double negatives, confusing 'cannot' and 'can not', and using 'incapable' when you mean current inability rather than lack of skill.

Avoid double negative: "I am not unable" cancels meaning and usually sounds wrong.
'Cannot' is one word. 'Can not' is rare and context-specific.
'Incapable' often implies a lack of ability or skill; 'unable' usually refers to a situation or current inability.

Quick edit checklist: 5-second test

Pick the best phrasing fast with this checklist.

1) Formal document? Prefer 'unable'.
2) Casual chat? Use "I'm not able" or "I can't".
3) Future event? Use "I won't be able".
4) Add a softener or brief reason for refusals or missed deadlines.
5) Offer next steps or an alternative when possible.

FAQ

Is 'I am not able' grammatically correct?

Yes. It's the negative form of the adjective 'able'. 'Unable' is an equivalent single-word adjective and is usually more concise.

When should I use 'unable' instead of 'not able'?

Use 'unable' in formal writing-business emails, reports, academic prose-for concision. Use 'not able' or contractions like "I can't" in speech, texts, or to soften refusals.

Can I say "I'm not able" in a professional email?

Yes. "I'm not able" is acceptable in many professional contexts, especially quick messages to colleagues. For more formal messages, use "I am unable."

Is 'unable to' always followed by an infinitive?

Yes. 'Unable' is normally followed by 'to' + verb: "She was unable to finish." To use a noun, rephrase: "She was unable to complete the task."

How can I rewrite 'I am not able to attend' politely?

Options: "I am unable to attend" (formal), "I'm afraid I can't attend" (polite), or "I won't be able to attend" (future). Add a brief reason or offer an alternative: "I am unable to attend due to a conflict; can we reschedule?"

Quick habit to build

When you see 'not able', decide: use 'unable' for formal clarity or a softer alternative for conversation. Practice rewriting a few sentences from your emails until the swap feels natural.

If you want automated feedback, paste a sentence into a grammar tool to see tone-specific suggestions and quick rewrites.