At the core of Avicenna’s ontology and metaphysics is the idea that existence is the indubitable base of reality. In other words, there is no doubt that there is existence; in an attempt to deny existence you prove your existence. If you are anything you are, if you are nothing you still are (nothing).

In the fourth class of Al-Isharat wa’l-tanbihat, On Existence and Its Causes, Avicenna explains why it is illogical to assume that metaphysics are not possible, i.e., that there is not a possibility of non-sensible reality. The people who hold this belief think that everything is reducible to human mental activity. In this case, one believes that things exist because they have entered one’s mind. This leads to not only having to accept that our senses are merely imagined, a sort of mental activity, but that one’s very intellect is a product of one’s imagination as well.

Avicenna queries: if everything is reducible to human mental activity, how about the principle of love? What are you feeling if you are in love and there are no sensibles? There clearly are essences that lay outside the sensibles such as love. Where do you locate love? If you reduce your world view to an empirical world of sensibles, there is no room for love, courage, compassion…