The Meaning of Essence According to Aquinas
             "...lest ignorance of them give occasion for error, and in order to lay difficulty concerning them, it should be said what 'essence' and 'being' mean (Aquinas 31-2)." This statement reflects the fact that essence is a complex theme, therefore, in order to understand the concept of essence, one must first know the definition of essence and also the definition of being. Since the definition of essence is not clearly stated, the only way to explain essence is to infer the meaning through the definition of being and through its relationship with complex and separated substances.
             Being is defined in two senses, one being essence and the other being the truth of propositions. A substance has being in the second sense if "an affirmative proposition can be formed of it, even if it posits nothing in reality (Aquinas 31)." This means that if it is said that pigs can fly they can because it was said and because it was said, then it is true. Because being in the second sense applies to just about everything, it has no substance because it encompasses all. Conversely, in order to be classified as being in the first sense or essence, a substance must have both matter and form except in the case of separated substances such as God and the "Intelligences". Matter and form are found in both simple and complex substances "...although more truly and nobly in the simple, which are the causes of the complex...(Aquinas 32)"
             As stated before complex substances have to have both matter and form in order to be called such. Without both matter and form they would not have their essence. In a complex substance their "...essence signifies what is composed of matter and form(Aquinas 33)." This means that the essence of a complex substance determines from what matter and in what form that specific complex substance will d
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