You can identify the קל form by applying these basic rules of thumb:

In the past tense, the three letters of the root appear first in the word. For example, in יָשַׁבְתִּי עַל הַכִּסֵּא (I sat on the chair), the three root letters appear (י.ש.ב), and only afterward, the suffix indicating I (תי). And unlike the פִּעֵל form, there is never a dot in the second letter of the root, in the past tense.

In the present tense, there is almost always an oh sound in the first syllable. Take, for example, the following verbs: אֲנִי קוֹרֵאת (I (f) am reading), אֲנַחְנוּ לוֹמְדִים (we are studying ), הֵן הוֹלְכוֹת (they (f) are walking), etc. The exception is when the second letter of the root is a ו or a י, in which case that letter drops and the oh vowel is lost.

Witness these patterns as you review the chart below, which lays out all the possibilities of the verb לִכְתּוֹב (to write) in past, present, future and imperative (command) tenses:

אֶכְתּוֹב כּוֹתֵב, כּוֹתֶבֶת כָּתַבְתִּי אני
נִכְתּוֹב כּוֹתְבִים, כּוֹתְבוֹת כָּתַבְנוּ אנחנו
כְּתוֹב תִּכְתּוֹב כּוֹתֵב כָּתַבְתָּ אתה
כִּתְבִי תִּכְתְּבִי כּוֹתֶבֶת כָּתַבְתְּ את
כִּתְבוּ תִּכְתְּבוּ כּוֹתְבִים כְּתַבְתֶּם אתם
כִּתְבוּ תִּכְתְּבוּ כּוֹתְבוֹת כְּתַבְתֶּן אתן
יִכְתּוֹב כּוֹתֵב כָּתַב הוא
תִּכְתּוֹב כּוֹתֶבֶת כָּתְבָה היא
יִכְתְּבוּ כּוֹתְבִים כָּתְבוּ הם
יִכְתְּבוּ כּוֹתְבוֹת כָּתְבוּ הן


As in any spoken language, things that are difficult for native speakers to pronounce get altered. So there will be roots that don’t fit into the neat table of קל above.