According to most historical textbooks Columbus made mistakes while measuring the size of the Earth. This led him to believe, that he can travel to India westwards in a reasonable time. This is however quite strange, that he let no one correct him in his mistake.
Could it be possible and was it ever considered by the historians, that Columbus was simply lying that he can find the way to India? That he knew about existence of Americas somehow and used the lie to get funding for his operation?
I think this is a valid question. But the answer is a rather resounding no. For one thing, we have no shred of evidence for such a conjecture. For another, this conjecture cannot be squared at all with the fact that Columbus to his dying day insisted on having actually landed in India - had he been dissimulating about his knowledge of the existence of America, surely after he got there he could have come clean.
The actual story how the great voyage was conceived is told with great detail (not all of it savoury) by Lord Acton in chapter 2 of his lectures on modern history.
