What is the object of reason (maf'ul lahu)?

In one line

Classical definition

Understand it

Say what was done, then say why. The why, expressed as a masdar in nasab, is the مَفْعُول لَهُ — also called مَفْعُول لِأَجْلِهِ.

سَافَرْتُ رَغْبَةً فِي الْعِلْمِ (safartu raghbatan fi al-'ilmi) — I travelled out of desire for knowledge. رَغْبَةً is not what I travelled; it is why I travelled.

The five mafa'il

Five roles share the word مَفْعُول, and each answers a different question about the action: what it fell upon, how much of it there was, why it happened, who it happened alongside, and when or where.

There is a condition English speakers miss. The masdar must be قَلْبِيّ (qalbi) — an inner one, something of the heart: desire, fear, hope, respect. Actions of the limbs will not serve. You may say “I stood out of respect”; you may not say “I came a walking” and mean it as a reason.

The test is simple: it must answer لِمَاذَا؟ (limadha), “why?”.

How to spot it

In the Qur'an

Don't confuse it with the absolute object

Do not confuse it with the مَفْعُول مُطْلَق.

Both are masdars in nasab, and that is where the likeness stops.

The مُطْلَق repeats the verb's own action — ضَرَبْتُ ضَرْبًا. It answers how, how much, what kind.

The لَهُ gives a different thing entirely: the motive — سَافَرْتُ رَغْبَةً. It answers why, and it must be a masdar of the heart.

Related terms

Common questions

How do I tell this from the other maf'uls?

By the question it answers. This one answers why. It is a verbal noun in nasab giving the reason the action happened, and the usual test is whether because of would sit comfortably in front of it in translation.