Frege and Kaplan on Reference

Frege: https://ia803206.us.archive.org/10/items/OnSenseAndReference/Frege%20-%20On%20Sense%20and%20Reference.pdf
More in-depth study guide: https://philopedia.org/works/on-sense-and-reference/

Kaplan: https://www.asc.ohio-state.edu/roberts.21/NYU/Kaplan.demonstratives.pdf
Short study guide: https://faculty.washington.edu/smcohen/453/KaplanDemoDisplay.pdf
A bit more: https://sandyber.github.io/philosophy/pdfs/phillang/2017/handout11.pdf