Allah’ın insan için en iyi olanı yapmasını ifade eden aslah düşüncesi Mu‘tezile’nin önemli ilkelerinden biri olmakla birlikte, aslahın kapsamı üzerinde Mu‘tezîlîler ihtilâf etmişlerdir. Basra Mu‘tezilesi’nin aslahı sadece dinî konularda geçerli kabul edip dünyevî konularda kabul etmemesine karşın, Bağdat Mu‘tezilesi hem dinî hem de dünyevî alanda geçerli kabul etmiştir. Ancak Basra Mu‘tezilesi’nin son dönemlerinde ortaya çıkan Hüseyniyye ekolü, aslahın dinî konular yanında dünyevî konularda da geçerli olduğunu söyleyerek Bağdat Mu‘tezilesi’nin görüşünü kabul etmiştir. Onlara göre Allah’ın dinî olsun dünyevî olsun her alanda aslahı yapmaya yönelik motivi (dâî) bulunmaktadır. Hüseynîler’e göre motivin varlığı fiilin varlığını zorunlu kıldığı için dünyevî konularla ilgili aslah da kaçınılmaz olarak meydana gelecektir. Buna karşın Basra Mu‘tezilesi’nin ana damarını temsil eden Behşemiyye ekolü ise dünyevî aslahın vâcip kabul edilmesinin sonu olmayan şeyin varlığa gelmesini gerektirdiğini, böyle bir şeyin ise imkânsız olduğunu söyleyerek dünyevî aslahın vücûbiyetini reddetmiştir. Konuya Hüseyniyye ekolünün bir taraftarı olarak yaklaşan İbnü’l-Melâhimî Behşemîler’in bu temel itirazını, sonu olmayan şeye motivin taalluk etmeyeceği ilkesinden hareketle reddeder. Zira motiv ancak özü itibariyle varlığa gelmesi mümkün olan şeye taalluk edebilir. Sonu olmayan şeyin ise varlığa gelmesi özü itibariyle mümkün olmadığı için hiçbir zaman buna motiv taalluk etmeyecek dolayısıyla da sonu olmayan şeyin varlığa gelmesi ihtimali asla gündeme gelmeyecektir. Ancak İbnü’l-Melâhimî’nin konuya yaklaşımındaki en özgün nokta her iki ekolü uzlaştırma teşebbüsüdür. Zira Basra ekolü her ne kadar dünyevî aslahın vâcip olduğunu söylemese de, Allah’ın buna yönelik motivi olduğunu kabul ettiklerinden dünyevî aslahın mutlaka varlığa geleceğini söylemiş olmaktadırlar. Diğer taraftan Bağdat ekolü ise dünyevî aslahın özünde vâciplik değeri bulunmadığını, dünyevî aslahın sadece Allah’ın cömertliği açısından vâcip olduğunu söylemektedirler. Yani Allah dünyevî aslahı, dünyevî aslah özünde vâcip olduğu için değil, cömert olduğu için yapmaktadır. Böylelikle her iki ekol de özünde vâcip olmayan bir şeyin sırf buna yönelik motiv bulunduğu için mutlaka varlığa geleceğini söylemiş olmaktadırlar.

The idea of aṣlaḥ, which implies that God necessarily acts to the advantage of humanity, was one of the principles of the Muʿtazila, although some scholars in this school disagreed on its meaning. Muʿtazilī scholars from Basra used the concept of aṣlaḥ only in regards to religious matters and disregarded it for mundane issues, whereas those from Baghdad employed it both for religious and mundane affairs. However, in a later period, a group of Muʿtazilīs from Basra, known as Ḥusayniyya, adopted the view of Baghdadi scholars in respect to its applicability to religious and mundane issues; thereby the Basra school of Muʿtazila also incorporated the idea of aṣlaḥ in its thought. The mainstream Basra school of Muʿtazila, the Bahshamiyya school, continued to insist on limiting the usage of aṣlaḥ only to religious matters by excluding mundane affairs completely. Therefore, the applicability of aṣlaḥ in mundane affairs became a point of dispute between the Bahshamiyya and the Ḥusayniyya in the later Muʿtazila period.The person who most clearly defined the Ḥusayniyya position in mundane aṣlaḥ and the critique of Bahshamiyya on the subject from the Ḥusayniyya perspective was Ibn al-Malāḥimī, who was the most significant scholar after Abū al-Ḥusayn al-Baṣrī, the founder of this school. Ibn al-Malāḥimī expressed his ideas on the issue in detail in his book al-Fāʾiq fī uṣūl al-dīn where he discussed the subject not through a dichotomy between Bahshamiyya and Ḥusayniyya, but rather in the context of two schools of Muʿtazila, the Baghdad and Basra schools. He identified his own position along the same line as the Baghdad school. According to Ibn al-Malāḥimī, the reason for the Bahshamiyya’s rejection of mundane aṣlaḥ was the idea that its existence necessitated that an eternal being come into existence. As one cannot imagine a finite aṣlaḥ in mundane matters, there will always be a more advantageous condition than the determined quality of the aṣlaḥ. Therefore, to consider mundane aṣlaḥ obligatory on God’s will means something eternal necessarily comes into existence. As an eternal being cannot come into existence, God cannot create a mundane aṣlaḥ. This idea would violate the principle of God’s obligations, which is not possible. Bahshamiyya scholars stated that mundane aṣlaḥ was not possible because it would always result in impossible outcomes.As for the Baghdad school (Ḥusayniyya), they approach the subject through the concept of dāʿī (motive). According to this school, there is a requisite relationship between the motive and the action. When a motive displays itself to the actor of the action, the actor unavoidably does the action. God’s knowledge of the mundane aṣlaḥ as beneficence towards this motive to do the mundane aṣlaḥ. When God knows the mundane aṣlaḥ as beneficial towards the person and carries through with the action, he is obliged to do it unless it has an evil result. In other words, the existence of the motive makes the existence of the action necessary; aṣlaḥ occurs necessarily for mundane affairs. The Ḥusayniyya school’s perspective of motive as the basis of mundane aṣlaḥ makes void the Bahshamiyya school’s primary point of rejection for the mundane aṣlaḥ with a proposition that eternity is to come into existence necessarily. However, since eternity cannot come into existence, the motive’s association to it, or in other words, the existence of a motive to realize eternity, is by nature impossible. As a motive to realize eternity never occurs, the Bahshamiyya school’s proposition for eternity’s coming into existence becomes void. Therefore, appearance of the mundane aṣlaḥ never requires that eternity comes into existence. The Ḥusayniyya school’s resolution in the later period inhibited later generations from adopting the hesitant attitude of the founder of the school Abū al-Ḥusayn al-Baṣrī as to whether mundane aṣlaḥ was to be accepted or not.However, the original point of view of the Ḥusayniyya School is based upon their effort to reconcile the two competing schools. Ibn al-Malāḥimī asserts that both schools expressed essentially the same opinion, though they expressed it differently; thereby, he held that their disagreement is only a literal one. The starting point for his reconciliation of the two schools is the motive towards action, which becomes the focus of the whole subject. According to Ibn al-Malāḥimī, members of the Basra School accept the mundane aṣlaḥ even if they do not say that the mundane aṣlaḥ (such as God’s beneficence) is necessary, because they accept that God has a motive towards it. On the other hand, the scholars of the Baghdad school state that the mundane aṣlaḥ does not carry a feature of necessity — it instead becomes necessary only in respect to God’s generosity. Therefore, God enacts mundane aṣlaḥ not because it is essentially necessary, but because of his generosity. All these entail that the Baghdad school, like the Basra school, adopts the view that something that is not essentially necessary comes into being just because the motive for it exists. The difference between them is this: the Basra school states that it comes certainly into being because of the motive even though they do not describe it by necessity. However, the Baghdad School states that a thing comes into being due to the motive even if it may not be due to itself. Therefore, both schools accept that the mundane aṣlaḥ does not have a feature of necessity by its essence, but it occurs certainly and due to the motive. The only difference is that while Baghdad scholars call this coming into being a necessity, the Basra scholars avoid explaining it that way. Therefore, the disagreement is literal.