In "philosophy, essence is the attribute or set of attributes that make an object or "substance what it fundamentally is, and which it has by "necessity, and without which it loses its "identity. Essence is contrasted with "accident: a property that the object or substance has "contingently, without which the substance can still retain its identity. The concept originates with Aristotle, who used the Greek expression to ti ên einai, literally 'the what it was to be', or sometimes the shorter phrase to ti esti, literally 'the what it is,' for the same idea. This phrase presented such difficulties for his Latin translators that they coined the word essentia to represent the whole expression. For Aristotle and his "scholastic followers the notion of essence is closely linked to that of definition (horismos) 
In the history of western thought, essence has often served as a vehicle for doctrines that tend to individuate different forms of existence as well as different identity conditions for objects and properties; in this eminently logical meaning, the concept has given a strong theoretical and common-sense basis to the whole family of logical theories based on the "possible worlds" analogy set up by "Leibniz and developed in the intensional logic from "Carnap to "Kripke, which was later challenged by "extensionalist" philosophers such as "Quine.
Ludwig Josef Johann Wittgenstein
(26 April 1889 – 29 April 1951) was an "Austrian
who worked primarily in "logic
, the "philosophy of mathematics
, the "philosophy of mind
, and the "philosophy of language
. Described by "Bertrand Russell
as "the most perfect example I have ever known of genius as traditionally conceived, passionate, profound, intense, and dominating,"
Wittgenstein is considered by many to be the greatest philosopher of the 20th century.
He helped inspire two of the century's principal philosophical movements: the "Vienna Circle and Oxford "ordinary language philosophy. According to an end of the century poll, professional philosophers in Canada and the U.S. rank both his "Tractatus Logico-Philosophicus (TLP) and "Philosophical Investigations among the top five most important books in twentieth-century philosophy, the latter standing out as "...the one crossover masterpiece in twentieth-century philosophy, appealing across diverse specializations and philosophical orientations".