The Qal stem derives from the Hebrew word קַל (qal), meaning "simple." It is the most basic form of the Hebrew verb and is therefore the default entry found in lexicons.
The characteristics of the Qal involve both voice and aspect. It is active in nature and can express a completed action (Perfect), an incomplete action (Imperfect), or a command. It may also appear as an infinitive or a participle—forms which are distinguished through changes in vowel patterns and affixation, the process of adding an affix (a prefix, suffix, infix, or circumflex) to a base or root word to change its meaning or function.
Using the root קָטַל ("to kill") as a paradigm:
• Perfect 3ms: קָטַל – “he killed”.
• Imperfect 3ms: יִקְטֹל – “he is killing / he will kill”.
• Imperative 2ms: קְטֹל – “kill!”.
• Infinitive Construct: קְטֹל – “to kill”.
• Infinitive Absolute: קָטוֹל – used for emphasis (e.g., “he will surely kill”).
• Participle Active: קֹטֵל – “killing”.
• Participle Passive: קָטוּל – “killed”.
The Qal is the stem from which all other stems (Niph’al, Pi’el, Pu’al, Hithpa’el, Hiph’il, Hoph’al) are derived by means of vowel changes, inflection, and doubling of consonants.