 Frege’s Begriffsschrift (1879) constitutes history’s first thoroughgoing attempt to formulate a rigorous formal system in which to carry out deductive reasoning. However, Frege did not see his Begriffsschrift as merely a tool for assessing the validity of arguments. Rather, he appears to have seen it as an organon for the acquisition of knowledge from unquestionable first principles; in addition he wanted to use it in order to help make clear the epistemic foundations on which our knowledge rests.  To this end his formal system contains not only symbols indicating the content of propositions (including logical constants), but also symbols indicating the force with which they are put forth. In particular, Frege insists that when using his formal system to acquire new knowledge from propositions already known, we use an assertion sign to indicate our acknowledgment of the truth of the proposition used as axioms or inferred therefrom. Frege thus employs what would now be called a force indicator: an expression whose use indicates the force with which an associated proposition is being put forth (Green 2002).