Sentence:  He first presented a complementary<!-- [sic] --> thesis on the <WSD>Enlightenment</WSD> philosopher Immanuel Kant (1724–1804), in which he used the term “archaeology” for the first time, and which indicated the period of history to which he was constantly to return./ The <WSD>Enlightenment</WSD>: the intellectual, philosophical, cultural and scientific spirit of the 18th century. A belief in reason, progress, man's “maturity” and a general rejection of tradition, religion and authority. 
Meaning of the word marked with <WSD> tags:  A 17th and 18th-century philosophical movement in European history; the Age of Enlightenment or Age of Reason emphasizing rationalism.