Laysa in Arabic means “not” (eg. that is not a pen). Unlike the other negations maa and laa, laysa is conjugated as a verb, depending on what you’re negating.
- the duck is not big (al-battatu laysat kabiyratan)
- the cat is not lazy (al-qittu laysa bi kaslaana)
Whenever you use laysa, the mubtada and khabr change: the mubtada becomes ismu laysa, and the khabr becomes khabru laysa.
Finally, laysa causes ismu laysa (not the mubtada–it’s now ismu laysa) to be marfoo’ (takes dumma/tanween-dumma), and khabru laysa becomes mansoob (takes fatha/tanween-fatha — see example one). Except if you prefix the khabr with bi (the preposition). In that case, it takes kasra, just as any word with a preposition. (Like example two.)
And of course, you can use laysa at the beginning of a sentence, just like any verb–eg. I am not sick (lastu bi mariydin).
The sarf for laysa is listed below–laysa is essentially a past-tense verb. (Read the sarf from top to bottom and right to left.)
Wallahu ‘alim. As usual, post a comment inshallah if you need any clarifications or have any questions.