Gottlob Frege

Gottlob Frege publishes 'Begriffsschrift', introducing predicate logic with quantifiers and establishing modern symbolic logic

Frege publishes Volume 1 of 'Grundgesetze der Arithmetik', attempting to derive arithmetic from pure logic

Bertrand Russell discovers Russell's Paradox in Frege's system, precipitating the foundational crisis in mathematics

Bertrand Russell discovers Russell's Paradox in Frege's system, creating a crisis in the foundations of mathematics

Russell writes to Frege informing him of the paradox in his logical system, devastating Frege's logicist program

Frege publishes Volume 2 of 'Grundgesetze' with an appendix acknowledging Russell's paradox and attempting a fix