A false premise is an incorrect or faulty statement or assumption on which an argument or belief is based. It means that the starting point or foundation of a discussion or reasoning is inaccurate or invalid. Full definition
Especially if, as I suspect, they're going to be mostly based on false premises. (redeeminggod.com)
Which brings us to the second false premise — that you can, or should, start from scratch. (bostonglobe.com)
The two sites referred to above start out from a clearly false premise: that scientists studying global warming have ignored the impact of water vapour. (newscientist.com)