Every trilateral Arabic root can (theoretically) be transformed into one of fifteen possible verb forms (أوزان awzaan). Each root has a general meaning (like "leaving," for example), and when you add a specific combination of letters to transform the root into one of the verb forms, that alters the meaning (like "making someone leave"). See below:
Most Arabic words are derived from a three-letter (trilateral) root. And each trilateral Arabic root can theoretically be transformed into one of fifteen possible verb forms (الأوزان, al-awzaan). (Forms 11 through 15 are very rare, so people usually just focus on forms 1 through 10, although 9 is also pretty rare). Each form has a basic meaning associated with the general meaning of the root being used. Here's a more detailed breakdown, using فعل (fa3ala, to do) as an example. (This is all taken from old handouts I got at the AUC, so it's not my original work.)
Form 1 - فعل (fa3ala)
Expresses the general verbal meaning of the root in question
||Form 1 verb
|خ ر ج (x-r-j) - leaving, departing
||خرج (xaraja) - to leave, go out
|ج م ع (j-m-3) - joining, uniting
||جمع (jama3a) - to gather, collect
|ع م ل (3-m-l) - doing, making
||عمل (3amala) - to work, to do, to make
|ق ط ع (q-T-3) - cutting
||قطع (qaTa3a) - to cut, cut off
|ب ع د (b-3-d) - separating, distance
||بعد (ba3ada) - to be far from
Form 2 - فعّل (fa33ala)
Built on form 1 by doubling the middle radical of the form 1 verb (adding a shadda to it)
Often is a causative version of the form 1 verb
خرج (xaraja) means "to go out"; خرّج (xarraja) means "to make (s.o.) go out; to graduate (s.o.)"
Often an intensive version of the form 1 verb (especially if the form 1 verb is transitive)
جمع (jama3a) means "to collect, gather"; جمّع (jamma3a) means "to amass, to accummulate"
Form 3 - فاعل (faa3ala)
Built on form 1 by adding an alif between the first and second radicals of the form 1 verb
Usually gives an associative meaning to the form 1 verb; describes someone doing the act in question to or with someone else
عمل (3amala) means "to work"; عامل (3aamala) means "to treat or deal with (s.o.)"
Form 4 - أفعل (af3ala)
Built on form 1 by prefixing an alif to the form 1 verb and putting a sukuun over the first radical
Similar to form 2 in that it is usually a causative version of the form 1 verb
خرج (xaraja) means "to go out"; خرّج (xarraja) means "to graduate (s.o.)"; أخرج (axraja) means "to expel, to evict; to produce"
Form 5 - تفعّل (tafa33ala)
Built on form 2 by adding the prefix تـ to the form 2 verb
Often a reflexive version of the form 2 verb
خرّج (xarraja) means "to graduate (s.o.)"; تخرج (taxarraja) means "to graduate" (Note: form 5 is usually intransitive)
Sometimes an intensive version of a form 1 verb
جمع (jama3a) means "to collect, gather"; تجمّع (tajamma3a) means "to congregate, to flock together"
Form 6 - تفاعل (tafaa3ala)
Built on form 3 by adding the prefix تـ to the form 3 verb
Usually a reflexive version of the form 3 verb
عامل (3aamala) means "to treat or deal with (s.o.)"; تعامل (ta3aamala) means "to deal with each other" (Form 6 is usually intransitive)
Form 7 - انفعل (infa3ala)
Built on form 1 by adding the prefix انـ to the form 1 verb
Usually a reflexive and/or passive version of the form 1 verb
قطع (qaTa3a) means "to cut, to cut off"; انقطع (inqaTa3a) means "to be cut off (from); to abstain (from)"
Form 8 - افتعل (ifta3ala)
Built on form 1 by adding the prefix ا to the form 1 verb and placing a sukuun must be placed over its first radical
Often a reflexive version of the form 1 verb
جمع (jama3a) means "to collect, gather"; اجتمع (ijtama3a) means "to meet; to agree (on)"
Sometimes has a specially derived meaning relative to a form 1 verb
بعد (ba3ada) means "to be far away"; ابتعد (ibta3ada) means "to avoid"
Form 9 - افعلّ (if3alla)
Built on form 1 by adding the prefix ا to the form 1 verb, placing a sukuun over its first radical, and adding a shadda to the last radical
Relates to colors
ح م ر (H-m-r) relates to "redness"; احمرّ (iHmarra) means "to become or turn red"
Form 10 - استفعل (istaf3ala)
Built on form 1 by adding the prefix استـ to the form 1 verb and inserting a ت between the first and second radicals; a sukuun must be placed over the first radical
Often a considerative version of the form 1 verb; means "to consider or to deem someone to have the quality" of the form 1 verb in question
بعد (ba3ada) means "to be far away"; استبعد (istab3ada) means "to consider s.o. or s.t. remote or unlikely"
Often a requestive version of a form 1 verb; means "to request or to seek something" for oneself
عمل (3amala) means "to make; to do"; استعمل (ista3mala) means "to use, to put into operation" (that is, to seek to make something work for oneself)
And here's a table of all the verb forms, including their perfect and imperfect conjugations (الماضي والمضارع), active and passive participles (اسم الفاعل واسم المفعول), and verbal nouns (المصدر). Because they're all regular and predictable (with the exception of form 1 - the second vowel in the imperfect and perfect conjugations, and the verbal noun), if you just memorize them, you'll know them for almost every verb there is. So if you're learning Arabic, I suggest you memorize all the verb forms along with their associated meanings as soon as you can; it'll really come in handy.
|مُفاعَلَة or فِعال