  Recognition that designating terms have a dual nature is far from recent. The Port-Royal Logic used terminology that translates as “comprehension” and “denotation” for this. John Stuart Mill used “connotation” and “denotation.” Frege famously used “Sinn” and “Bedeutung,” often left untranslated, but when translated, these usually become “sense” and “reference.” Carnap settled on “intension” and “extension.” However expressed, and with variation from author to author, the essential dichotomy is that between what a term means, and what it denotes. “The number of the planets” denotes the number 9 (ignoring recent disputes about the status of bodies at the outer edges of the solar system), but it does not have the number 9 as its meaning, or else in earlier times scientists might have determined that the number of planets was 9 through a process of linguistic analysis, and not through astronomical observation. Of the many people who have contributed to the analysis of intensional problems several stand out. At the head of the list is Gottlob Frege.