It might sound like a small, furry animal or an exotic fruit but in philosophy a lemma is a philosophical statement that you accept as true in order to find out whether another statement is true.
So, that’s a lemma but why should there be no false ones?
To start with, what’s knowledge? Something you feel? Something you believe?
Plato thought it was something you believe is true, is true and you have some justification for believing it to be true. I believe it’s 10 am, it is 10am and that clock says it’s 10am. Sounds pretty sensible and people thought that way for a few thousand years until 1963 when a bloke called Edmund had a free afternoon a decided it was all rubbish. You might believe it to be 10am, it might actually be 10am and that clock might say it’s 10am but what if the clock has stopped and you just got lucky. You can’t say you knew it was 10am if you were looking at a stopped clock.
That upset a lot of philosophers and they have been trying to prove Edmund wrong ever since. Not that he seemed to care. He never discussed it again. One idea put forward is that it’s ok as long as your belief is not deduced by something that isn’t true – a false lemma. The No False Lemmas account of knowledge. Philosophers are still arguing about this and boy do they like to argue! If you are interested, you can find more about it here – https://plato.stanford.edu/entries/knowledge-analysis/#NoFalsLemm
It’s about knowledge. What is true? What is false?