Al-Sabab is a sign whose presence necessitates the existence of a Hukm and that which, if absent, necessitates an absence of that Hukm. It is not the motive behind the legislation of the Hukm. Hence, al-Sabab is related to the existence of the Hukm in reality. It is not related to the legislation of the Hukm to deal with reality. The sighting of the month of Ramadhan is the Sabab for the obligation of fasting upon those who sight it: “So every one of you who is present (at his home) during that month should spend it in fasting.” [2-185]
Hence, al-Sabab indicates the presence of the obligation, not the motive nor the reason for the obligation. The presence of the obligation is different to the reason for the obligation. Al-Sabab is contrary to the Illah, which is the matter for whose sake the Hukm has come into being – in other words, it is the motive behind the legislation of the Hukm. Thus, it is related to the legislation of the Hukm and not related to its effective presence. Hence, al-Illah is the reason for the obligatory nature of the Hukm and not the reason for its existence.
Al-Sabab comes before the existence of the Hukm. If it materialises, the execution of the Hukm becomes compulsory. Before the existence of al-Sabab, the Hukm is obligatory on the liable; however, the presence of this obligation depends on the existence or the materialisation of al-Sabab. This is contrary to al-Illah, which accompanies the legislating of the Hukm, for it is the motive behind its legislation. For instance, the sighting of the moon of Ramadhan is al-Sabab for the existence of the obligation of fasting; thus it precedes the fasting. This is contrary to the public waterfalls that generate electricity, which represent al-Illah to make electricity a public property; it accompanies the legislating of the Hukm. The fact that the waterfalls are public property accompanies the Hukm of the electricity generated from them, that being public property, which is the motive behind the Hukm.
Moreover, al-Sabab is specific to the reason for its existence and it does not go beyond it to other matters, thus no analogy can be made. Al-Illah, however, is not specific to the Hukm that has been legislated for its sake; it exceeds it to other matters and analogy can also be made on al-Illah itself. For instance, the time of Salat al-Maghreb is al-Sabab for the existence of Salat al-Maghreb and not the reason for obligating it. Also, it is not valid as al-Sabab for other than Salat al-Maghreb; thus no analogy can be made on it. However, the fact that distraction from Salat acts as al-Illah for the legislating of the Hukm prohibiting trade during the Athan of Salat al-Juma’a, as indicated by Allah’s (swt) saying: “If the call for prayer…”, this is not specific to trading but can also extend to other matters, in which case the Hukm goes beyond it to include this other matter. Hence, it is through al-Illah that analogy is made on the Hukm of trading, making for instance hiring, swimming and writing prohibited during the Athan of Salat al-Juma’a. Hence, al-Illah is the motive behind the legislating of the Hukm, whereas al-Sabab is the motive behind the effective occasioning of the rule, i.e. when to perform it.
Therefore, Allah’s (swt) saying: “Establish prayer according to the movement of the sun” is not an Illah but rather a Sabab, because the movement of the sun is al-Sabab for establishing the Salat and not al-Illah. It was also reported that Aisha (ra) said: “The sun eclipsed during the lifetime of the Messenger of Allah (saw), so he ordered someone to call for a collective prayer and then he stood and prayed four Raka’at (bowings) in two Raka’at and four Sajdat.” This is not an Illah but rather a Sabab, because the eclipse of the sun is a Sabab for establishing prayer and not an Illah for it. It has been also reported on the authority of Salama Ibnul Akwaa that “We used to pray the Maghrib prayer with the Prophet when the sun disappeared from the horizon”, which is not an Illah but rather a Sabab, because the disappearance of the sun behind the horizon is a Sabab to establish the Maghrib prayer and not an Illah for it. All this and the like is part of the Sabab(s) and not the Illah(s) because the descent of the sun from its highest point in the sky, its eclipse and its disappearance from the horizon are each a Sabab for the effective materialisation of the Hukm and not a reason for its obligation; i.e. a Sabab for its execution by the Mukallaf (liable) and not a reason for its legislation. Hence, it transpires that what has been mentioned about the rituals in terms of being Sabab(s) and not Illah(s) makes the rituals rigidly subject to text (tawqifiyah): they cannot have an Illah and no analogy can be made on them. This is because the Sabab is specific to what it has been designated to be a Sabab for, which is in order to establish the rule and not to legislate it.