A colleague mentioned that while doing exams (in China) for academic English, using the word 'then' after an 'if' was marked as incorrect.
For example, "If it is raining then I will need my umbrella" vs "If it is raining, I will need my umbrella".
He thought this was because it was grammatically incorrect, however I have found other questions here that indirectly refute that. For example Can I use an if clause without then.
Is this a case of informal vs formal English instead?