I'm trying to find the correct way to answer a question asking for a reason. I've searched here and the net but not been able to find the answer, probably because I do not how to search correctly. I've asked OpenAI and got an answer, but I'm not sure that its answer is correct. So, I'd like to have opinions here. It's like this:

If the fact is that humans are intelligent because they have well-developed brains, then if someone asks "why are human intelligent?", which of the following answers is grammatically correct or better?

1.The answer is because humans have well-developed brains.

2.The answer is that humans have well-developed brains.

  • N.B. OpenAI said that both answers are grammatically correct but slightly differ in usage. For me, I'm certain that answer 2 is grammatically correct, but I'm not so sure that answer 1 is so although, for me, it sounds to me better than answer 1.
    – user287279
    May 31 at 5:47
  • 1
    2 is the better option. The use of "because" in 1 could be accepted in common speech, but is not ideal grammar.
    – ralph.m
    May 31 at 9:40
  • 1
    Usually we say The answer / reason / explanation is that [assertion], but ...is because [assertion] does occur (especially with reason, rarely with explanation). But the less common forms are just that - "less common". They're not "syntactically invalid". May 31 at 12:20
  • It's a weird question, and seems confused about cause and effect. Humans aren't intelligent because they have well-developed brains; having well-developed brains is the outcome of a process that led to humans being intelligent. It's like the old joke "Why do giraffes have long necks?" "Because their heads are so far off the ground."
    – Stuart F
    May 31 at 12:43
  • Thank you very much for all the comments. However, @StuartF , this question is about grammar not science, and if you please notice the text, you'll see that there is no assertion about a connection between human intelligence and the brain. It's just a conditional sentence used as an example to ask about a grammar problem.
    – user287279
    May 31 at 16:56

1 Answer 1


I can't find supporting evidence in a standard grammar, but I'll put down my views.

  • 1'. The answer is: because humans have well-developed brains.

uses a quote structure with The answer is instead of the typical He said as the dialogue tag. Some might require an introductory colon (as here) or comma, but zero punctuation is often preferred nowadays where the actual quote is otherwise offset (by inverted commas or italicisation). No offsetting at all, as in the original, looks at best informal, arguably unprofessional. Some might italicise (though capitalisation would probably be eschewed):

  • 1''. The answer is because humans have well-developed brains.

Internet examples (in a Google search for "The answer is because") include the use of the offsetting comma, a dash, a colon, a comma with inverted commas and capitalisation, a comma with inverted commas and lower case ....

Some would also prefer a complete sentence rather than a fragment (when not reporting a speaker's exact words), but few get really exercised about the judicious use of fragments nowadays.


  • 2'. The answer is that humans have well-developed brains.

uses a report structure in standard fashion, with The answer is that as the introductory clause in place of the prototypical She said that. What follows the complementiser that is unproblematically an independent clause. This looks better than [1] in formal settings (at least).

  • Thank you very much.
    – user287279
    May 31 at 16:57

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