Friedrich Engels (1820-95)
Ludwig Feuerbach (1804-72)
Gottlob Frege Creator of the system of modern symbolic logic. His work went virtually unnoticed in the 19th century. It was brought to light by Bertrand Russell, who discovered that Frege's system harbors an inconsistency, "Russell's paradox." Frege's work is covered in part in Philosophy 137, Philosophy of Language.
Ernst Mach (1838-1916)
Meinong
Friedrich Schleiermacher (1768-1834)
George Boole (1815-64)
F. H. Bradley (1846-1924)
Sir William Hamilton (
John Stuart Mill (1806-73) Ethicist, political philosopher and logician. Two of his most celebrated works can be found on-line: On Liberty
Augustus de Morgan
Ralph Waldo Emerson (1803-82)
Henry David Thoreau (1817-62)