The view of nature we adopt in the natural attitude is determined by common
sense, without which we could not survive. Classical physics is modelled on
this common-sense view of nature, and uses mathematics to formalise our natural
understanding of the causes and effects we observe in time and space when we
select subsystems of nature for modelling. But in modern physics, we do not go
beyond the realm of common sense by augmenting our knowledge of what is going
on in nature. Rather, we have measurements that we do not understand, so we
know nothing about the ontology of what we measure. We help ourselves by using
entities from mathematics, which we fully understand ontologically. But we have
no ontology of the reality of modern physics; we have only what we can assert
mathematically. In this paper, we describe the ontology of classical and modern
physics against this background and show how it relates to the ontology of
common sense and of mathematics