[The word ‘Being’] is applied to objects in virtue of that primary perfection signified by the verb ‘to be,’ as understood in the first of the senses mentioned …, namely ‘to exist.’ The notion which expresses this primary characteristic of ‘Being’ or ‘actuality,’ is clear to us from the dawn of our intelligence. It is absolutely simple. We cannot explain it by any that is simpler: for its simplicity is ultimate. Indeed were there not primary notions of this kind, it would be impossible to explain anything. The mind would be lost in an infinite regress, as it endeavoured to find some idea which did not itself need elucidation.
George Hayward Joyce, S.J., Principles of Logic, London: Longmans 1916