Frege doesn’t have an independent and comprehensive issue concerning indexical semantics. However, in some of his works, especially “The Thought”, he has declared some characteristics of some indexical. In sum, his view is that if a sentence contains an indexical word, it has linguistic meaning; However, it does not express a Thought (=sense) unless the reference of that indexical word is determined. Regarding Frege’s views concerning the characteristics of Thought, it seems his approach to the semantic of indexical can be extended to be true concerning other expressions having concrete references. To obtain a thought, all temporal and spatial constraints should be considered. Hence, we may claim that Frege considers all expressions with concrete references indexical.
1- Caplan Ben (2007), “On sense and Direct Reference”, pp.2-16, in “Sense and Direct Reference, Readings in the Philosophy of Language”, ed. Matthew Davidson, The McGraw Hill Companies
2- Dummett Michael (1973), Frege, Philosophy of Language, 2nd. Ed., London, Duckworth
3- Frege Gottlob (1892), “On Sense and Reference”, pp.56-78, in Translations from the philosophical writings of Gottlob Frege, 3rd. ed., eds. Geach P.T., & Black M., Basil Blackwell, Oxford, 1952
4- Frege Gottlob (1918), The Thought: A Logical Inquiry, in Mind, Vol.65, No. 259, Jul. 1956, pp.289-311
5- Mill John Stwart (1843), A System of Logic Ratiocinative and Inductive Being a Connected View of the Principles of Evidence and the Method of Scientific Investigation, University of Toronto Press, Routledge & Kegan Paul, 1974
6- Salmon Nathan, (2007), “ Frege’s Puzzle”, pp. 280-326, in Sense and Direct Reference, Readings in the Philosophy of Language, ed. Matthew Davidson, The McGraw Hill Companies
7- Searle John (1969), Speech Acts, CPU
Caplan B (2007). On sense and direct reference. In: Davidson M. On sense and direct reference: Readings in the philosophy of language. New York: The McGraw Hill Companies. p. 2-16. [Link] [DOI:10.1111/j.1747-9991.2006.00014.x]
Dummett M (1973). Frege: Philosophy of language. 2nd edition. London: Duckworth. [Link]
Frege G (1892). On sense and reference. In: Geach PT, Black M, editors. Translations from the philosophical writings of Gottlob Frege. 3rd edition. Oxford: Basil Blackwell. p. 56-78. [Link]
Frege G (1918). The thought: A logical inquiry. Mind. A Quarterly Review of Psychology and Hilosophy. 65(259):289-311. [Link] [DOI:10.1093/mind/65.1.289]
Mill JS (1843). A system of logic, ratiocinative and inductive: Being a connected view of the principles of evidence, and the method of scientific investigation. London: Cambridge University Press. [Link] [DOI:10.5962/bhl.title.25118]
Salmon N (1986). Frege's puzzle. In: Davidson M. On sense and direct reference: Readings in the philosophy of language. Cambridge: The MIT Press. p. 280-326. [Link]
Philosophical Thought