For: Existentialism

In common usage, existence is the world of which we are aware through our senses, but in philosophy the word has a more specialized meaning, and is often contrasted with essence. Philosophers investigate questions such as "What exists?" "How do we know?" "To what extent are the senses a reliable guide to existence?" "What is the meaning, if any, of assertions of the existence of categories, ideas, and abstractions."

The word "existence" comes from the Latin word 'existere', meaning to appear or emerge or stand out.

The word 'exist' is certainly a grammatical predicate, but philosophers have long disputed whether it is also a logical predicate. Some philosophers claim that it predicates something, and has the same meaning as 'is real', 'has being', 'is found in reality', 'is in the real world' and so on. Other philosophers deny that existence is logically a predicate, and claim that it is merely what is asserted by the etymologically distinct verb 'is', and that all statements containing the predicate 'exists' can be reduced to statements that do not use this predicate. For example, 'A Four-leaved clover exists.' can be rephrased as 'There is a clover with four leaves.'

This philosophical question is an old one, and has been discussed and argued over by philosophers from Aristotle, through Avicenna, Aquinas, Scotus, Hume, Kant, Kierkegaard and many others.

In mathematical logic existence is a quantifier, the "existential quantifier", symbolized by ∃, a backwards capital E. To symbolize "Four leaf clovers exist," mathematicians would first define predicates, P(x) = "x is a clover" and Q(x) = "x has four leaves", and then form the well-formed formula (∃x)(P(x) and Q(x)).

Historical conceptions

In the western tradition of philosophy, the first comprehensive treatments of the subject are from Plato's Phaedo, Republic, and Statesman and Aristotle's Metaphysics, though earlier fragmentary writing exists. Aristotle developed a complicated theory of being, according to which only individual things, called substances fully have being, but other things such as relations, quantity, time and place (called the categories) have a derivative kind of being, dependent on individual things.

The Neo-Platonists and some early Christian philosophers argued about whether existence had any reality except in the mind of God. Some taught that existence was a snare and a delusion, that the world, the flesh, and the devil existed only to tempt weak humankind away from God.

The medieval philosopher Thomas Aquinas, perhaps following the Persian philosopher Avicenna, argued that God is pure being, and that in God essence and existence are the same. At about the same time, the nominalist philosopher William of Ockham, argued, in Book I of his Summa Totius Logicae (Treatise on all Logic, written some time before 1327) that Categories are not a form of Being in their own right, but derivative on the existence of individuals.