1.The reason she’s so irritable is because she’s tired.

2.The reason she’s so irritable is because of that she’s tired.

Is there any difference in meaning between 'because' and 'because of that'?

Would anybody like to tell me the difference?

  • because of wants a noun-phrase complement. It does not accept a that-clause complement.
    – TimR
    Nov 1, 2016 at 11:27

3 Answers 3


Because is a subordinating conjunction, which means it introduces a new subordinate clause. Your example

The reason she’s so irritable is because she’s tired.

Is correct

Because of is prepositional. It needs a direct object, not a that-clause

The reason she’s so irritable is because of her work.

Is correct.

P.S: For me, the usage of "because" is redundant here. You have "The reason" in front of your sentence, so introducing the reason with "because.." is not necessary.


Your two sentences are best rendered in this way:

1.She’s so irritable because she’s tired.

Here the reason ... is is redundant, since you use because afterwards.

2.The reason she’s so irritable is that she’s tired.

Here it is because of is redundant (and it would require a noun or a noun phrase anyway), but that is used correctly.

Note: In a more formal way you could say

The reason of her irritability is her tiredness.


Actually, "because" shows the reason for something, so the first sentence would be best without the "reason" in the first half, as previously pointed out. (see: https://dictionary.cambridge.org/dictionary/english/because)

The phrase "because of that" usually shows the result of something so the second sentence is wrong, and could be rephrased as:

She is tired. Because of that, she is very irritable.

However, this would sound better if it were more developed, as in: She finds her job and the commute to and from work exhausting. Because of that, she is usually very irritable when she gets home.

see: https://www.wordhippo.com/what-is/another-word-for/because_of_that.html

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