Rule of the One: Avicenna, Bahmanyār, and al-Rāzī on the Argument from the Mubāḥathāt


Avicenna is a strong proponent of what some of the later ones call qā ͑idat al-wāḥid or ‘rule of the one’ (RO). The gist of RO states: from the one only one directly proceeds. In the secondary literature, discussion of this Avicennian rule is usually limited to a particular application of it i.e., the issue of emanation. As result, it’s not really clear what RO means, nor why Avicenna endorsed it. In this paper, I try and remedy this situation by doing two things – one on the taṣawwur front, the other on the tasdīq. First, explain just what the terms of RO amount to – that is, its subject and predicate. In doing this, I distinguish between a narrow and a broad understanding of RO, and the show that, on the Avicennian view, the scope of RO is broad; it is meant to be a general principle of efficient causality. This is why it is appealed to in various contexts to establish substantial philosophical theses. Second, I consider an argument Avicenna offers for RO in the Mubāḥathāt. In unpacking it, I uncover some of its realist presuppositions, and then further clarify it in light of a critique first raised by Bahmanyār and then later made famous by Fakhr al-Dīn Rāzī. I then conclude by seeing whether the Avicennian has the resources within the initial premises of the argument to meet the objection that’s raised.


Avicenna Bahmanyār Mubāḥathāt Rule of the one qā ͑ida al-wāhid Rāzī Ṭūsī efficient causality causal procession tanbīh self-evident