In his monumental work al-Shifa (or the Cure), Ibn Sina (980-1037) has conducted a deep investigation into the concept of number whose status was left in disarray since the discovery of the irrationals. Unlike the Greek tradition which unanimously rejected the irrationals, arab mathematicians, since the pioneering work of al-Khwarizmi’s Book of algebra, accepted the irrationals as numbers throwing into confusion the narrow classical understanding of the concept of number. Much ahead of theoretical research, the rapid development of mathematical practice since the ninth century has shown that the definition of number should be updated and its understanding clarified. It is in this context that Ibn Sina has carried out his major investigation into the foundations of mathematics. In his paper “Philosophy of mathematics”, Roshdi Rashed explains how Ibn Sina’s al-arithmatiqi radically shook up the ancient classification of the four mathematical disciplines with the aim of making them independent of natural philosophy: “from now on, he concludes, all the ontological and cosmological considerations which burdened the notion of number are de facto banned from al-arithmatiqi, considered thus as science.” Ibn Sina’s main objective to make arithmetic a pure science independent of natural philosophy is only the beginning of the story. But by what means? Here is the crux of his argument: 1) numbers are objects: this is their function in mathematical practice; 2) since they have no existence in the outside world, they exist in our mind not as real but simply as intentional objects. And the tough question in this regard is: how can a number such as 7 e.g. be an object of the mind? Or more generally what does it mean for pluralities to be the object of an intentional act? I shall investigate the answer given by the author of al-Shifa to these questions and examine to what extent it can be compared to some of the various attempts made by the 19th century mathematicians and philosophers.