Page "Ramsey–Lewis method" Paragraph 2

However, some of those statements in a theory refer to other unobserved entities and properties such as " charge " or " spin ".

For instance, " Electrons attract protons " and " Electrons have negative charge " employ the terms " protons " and " negative charge " ( with the latter also implicitly using the concept of " charge ").

These properties are formalized, statements ( such as conditionals are formed using them, and those statements taken together are the definiens of the term.