Emmanuel Joseph Sieyès (3 May 1748 – 20 June 1836), most commonly known as the abbé Sieyès (French: [sjej?s]), was a French Roman Catholic abbé, clergyman and political writer.
He was one of the chief political theorists of the French Revolution, and also played a prominent role in the French Consulate and First French Empire.
His 1789 pamphlet What Is the Third Estate? became the manifesto of the Revolution, helping to transform the Estates-General into the National Assembly in June 1789.
He was offered a position on the French Directory, but turned it down.
After becoming a director in 1799, he was among the instigators of the coup d'état of 18 Brumaire (9 November), which brought Napoleon Bonaparte to power.
He also coined the term "sociologie" in an unpublished manuscript, and made significant theoretical contributions to the nascent social sciences.