Alright and All Right

The Quick Answer
What is the difference between alright and all right?

Alright is a nonstandard variant of all right.
Even though alright is becoming more acceptable, it is best avoided in formal writing.

Alright Is Still Not Widely Accepted

Many people use alright unaware that it is not universally accepted as a word. It should be written all right. However, the merger of all right to alright has been underway for over a century, and it is becoming more acceptable. Mergers such as altogether and already are fully acceptable. They are far older than alright.

It's Not Right, and It's Not Wrong

Interestingly, the Microsoft Word spellchecker will not highlight alright as an error, but it will also not suggest alright if you spell it incorrectly.

Therefore, Microsoft is sitting on the fence with regard to alright being accepted as standard.

MS Word does not show alright as an error and does not offer alright as an option.

Alright is Deemed More Modern by Some

Some would even argue that, through common usage, alright is becoming more acceptable than all right. The makers of TV show "It'll Be Alright on the Night" are known to have considered "It'll Be All Right on the Night" but opted for the former as a more modern version.
Interactive Exercise
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See Also

adverse or averse? affect or effect? appraise or apprise? avenge or revenge? bare or bear? complement or compliment? dependant or dependent? discreet or discrete? disinterested or uninterested? e.g. or i.e.? envy or jealousy? imply or infer? its or it's? material or materiel? poisonous or venomous? practice or practise? principal or principle? tenant or tenet? who's or whose?
Common errors in writing Easily confused words