When confronted with hypothetical systems in Arabic, one inevitably meets, at one time or another, a fāʾ between the protasis (p) and the apodosis (q). We do not fail to note, however, that its presence does not seem to indicate identical relationships between p and q. According to Larcher, for whom fāʾ has a unique role, that of a segmentator, this particle is the mark of a double break, formal and semantic: as soon as fa- is present there is no logical relation of implication between p and q, the logical relation possibly being of another nature. Within the framework of the global vision that he offers, Larcher then recognizes this particle with several semantic values (deductive, enunciative, justificative, oppositive). This article attempts to answer the question of whether the Arabic grammar recognizes also several semantic values attached to the segmentator fāʾ. Through the prism of this study of the history of Arabic grammar, it will be shown that at least two values are recognized in fāʾ: one, called fāʾ al-sababiyya, is easily recognized by the Arabic grammatical tradition and marks the relationship of logical implication where p induces q; the other, known as fāʾ al-taʿlīl, marks on the contrary something else and in particular, but not only, that it is in fact q which is the cause of p. However, this value and its denomination of fāʾ al-taʿlīl, besides being ignored by the Arabists, is largely also by the Arab grammarians themselves: it is in fact only recognized in a more or less explicit manner among certain medieval grammarians, and is only specifically named as such very recently with Ġalāyīnī (d. 1364/1944). It rather seems that this value is in fact derived from the foundations of law (ʾuṣūl al-fiqh) in the 5th/11th century, and that its denomination dates at least from the 8th/14th century in the same field. All of this is later found in another of the sciences related to Arabic grammar, namely that of exegesis (tafsīr), at least in the 12th/17th century. This then shows all the interest in pursuing transdisciplinary works for the case of Arabic grammar.