• philosophy of physics
• quantitative
• semantic view of theories
• simplicity
• syntactic view of theories
• theoretical virtues

The theoretical virtue of simplicity is widely recognized by philosophers and scientists as one of the most significant selection criteria for determining the adoption of a theory from an empirically underdetermined collection of candidates. In philosophy of physics two different meanings of it can be distinguished, syntactic (concerning the complexity of descriptions of a physical situation) and semantic (concerning the referents of the theory). In particular, the semantic aspect of simplicity turns out to be discussed less frequently than its counterpart in the literature on the subject of theoretical virtues. This kind of simplicity can be further distinguished into quantitative (pertaining to the number of objects in a theory) and qualitative (pertaining to the number and complexity of properties affecting the objects). What is argued in the text is the existence of a trade-off between these two types, with maximization of one resulting in minimization of the other and vice versa. In conclusion, a series of case studies from the history of physics are offered that testify to the alternating fortunes of one type over the other.