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.

For example:

  1. the duck is not big (al-battatu laysat kabiyratan)
  2. 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.)

<th>
  I (M/F)
</th>

<th>
  You (F)
</th>

<th>
  You (M)
</th>

<th>
  She (F)
</th>

<th>
  He (M)
</th>

<th>
</th></tr> 

<tr>
  <td>
    لَستُ
  </td>

  <td>
    لَستِ
  </td>

  <td>
    لَستَ
  </td>

  <td>
    لَيسَت
  </td>

  <td>
    لَيسَ
  </td>

  <th>
    Single
  </th>
</tr>

<tr>
  <td>
    لَسنَا
  </td>

  <td>
    لَستُمَا
  </td>

  <td>
    لَستُمَا
  </td>

  <td>
    لَيسَتَ
  </td>

  <td>
    لَيسَا
  </td>

  <th>
    Dual
  </th>
</tr>

<tr>
  <td>
  </td>

  <td>
    لَستَنَّ
  </td>

  <td>
    لَستُ
  </td>

  <td>
    لَسنَ
  </td>

  <td>
    لَيسُو
  </td>

  <th>
    Plural
  </th>
</tr>

Wallahu ‘alim. As usual, post a comment inshallah if you need any clarifications or have any questions.