  In this paper, the theoretical terms of contemporary cosmology are examined
as intellectual artefacts. An ontology and methodology are introduced for this
purpose, which includes defining the concept of a hypothetical object.
Introducing a hypothetical object is contrasted with the modification of
physical laws as alternative ways of explaining the discrepancy between
observations and theoretical predictions. Historical examples of theory choice,
which involved these alternatives, are discussed. This is followed by a study
of theory choice in contemporary cosmology. In particular, the focus is on the
case of dark matter and modified gravity as alternative explanations for
observed mass discrepancies in galaxies and galaxy clusters. These alternatives
are analyzed, and their similarities and differences to the historical examples
are pointed out.
