Is the following sentence grammatically correct? If I would have known, I would have come.

Analysis:

The sentence uses the third conditional structure, which describes a hypothetical situation in the past and its hypothetical consequence in the past. The correct structure for the 'if' clause in the third conditional is the past perfect tense ('had' + past participle).

Correction:

The correct sentence is: 'If I had known, I would have come.'

Answer: The sentence is grammatically incorrect. The correct form is 'If I had known, I would have come.'