Cogitosus a monk of Kildare, is commemorated on April 18, in the Mart. Tallaght, where he is called "the wise." There is great diversity in the dates of his life, as given by different writers, but Lanigan and Petrie prove incontestably that Cogitosus must have written previously to A.D. 831, when Kildare was first plundered, and must have flourished at latest in the beginning of the 9th century (Lanigan, Eccles. Hist. of Ireland, 1:379 sq.).