For Aristotle, being (Greek: ouisia) was a substance (Latin: substantia, from sub under stare to stand.) In order to know the essence of a substance; that is, what a thing is, its essence must be demonstrated in a definition, Aristotle said. His most famous example of this is his definition of a human being as a rational animal. However, to define is to set limits on something (Latin: definire, from de completely finire to bind or set limits on, from finir boundary or end.) When Aristotle argues that knowledge of essences is gained via definitions he is linking his metaphysics of substance to his epistemology by making knowledge the result of capturing the essence of a substance in a definition. Heidegger would later criticize Aristotle for obscuring being by confusing it with substance. Still later, two of Heidegger’s students, Emmanuel Levinas and Xavier Zubiri would take up this critique of Aristotle.
It is important to point out that both Levinas and Zubiri were ethnic minorities. Levinas, a Lithuanian Jew and Zubiri, a Basque Catholic priest (who was later secularized). Each of these thinkers felt the sting of being totalized in definitions of the dominant cultures within which they lived and found themselves marginalized from. Levinas‘ privileging of the other arises against the background of his status as an ethnic minority in Europe. Zubiri’s emphasis on the dynamic structure of reality as the ground of being, which is incapable of being captured in a definition, also arises against the backdrop of his Basque heritage. (This is my contention that I am still investigating)
Levinas finds the other caught in a tension between its infinity (undefinability) and its totality (definability). However, his account of the infinity is not sufficiently accounted for, in my opinion (this may be the result of my limited reading.) Zubiri, on the other hand, does provide an account for it. Against Aristotle, Zubiri claims that reality is not a substance but rather it is a substantivity; that is, reality is not a static essence able to be captured in a definition but instead it is a dynamic structure of notes that is undefinable and full of possibility. For Zubiri, the history of philosophy has failed to recognize the distinction between reality as it is apprehended and naked reality which is not yet framed in concepts. Aristotle’s analysis stops at apprehended reality or in Levinasian terms totalized reality. But as Levinas reminds us, to totalize the other in this way is a cruelty that does violence to the other. For Zubiri, it is simply unscientific (given the insights from quantum physics) to think that reality can be exhausted in a demonstration or a definition. Zubiri reminds us that reality is dynamic and possibilating. Levinas reminds us that love is an insomniac and never falls asleep at the wheel (which leads to terrible accidents!) To capture the other in a definition is to enslave the other and relinquish pursuit of the possibilating mystery of the other.
I am still working out the connection between these two thinkers and there relationship to the other. I invite your comments, suggestions, and corrections.