Promio to have one better agreement of the considered subject, being and essencia, having in consideration the human cognitivo process, Toms Saint de Aquino in its workmanship the Being and the Essence, considers that if it leaves of what it is more easy thus to extract the knowledge of ' ' simples' ' for ' ' composto' ' arriving it what it is previous, breaking itself of the posterior one. Agreeing to Avicena, that the being and the essence are what first the intellect conceives, and observing as Aristotle that a small error in the principle can become great the end, Toms Saint de Aquino propoe to eliminate it eventual difficulties due to clarity of the concepts of being and essence, marking itself this to say what ' ' if he understands for the terms essence and ente' ' , as one meets in diverse meanings, that is, from its conception as concept while he enunciates yourself in the truth of the proposals and what refers to the ten predicamentos as well as if he relates with the universal logical intentions of sort, species and difference. Chapter I the principle, Toms Saint detaches in the Metaphysics of Aristotle the ways as the being if it says for itself, being two these ways: divided in the ten categories and concerning the truth of the proposals, way where the privations and negations can be said beings, therefore its distinction in the first way is to be affirmative despite it does not add nothing the thing. Following the thought of Avicena, Toms Saint de Aquino, affirms that the essence of the thing is meant by the being said in the first way, the divided one for ten categories, where the essence must be common to all these natures where the beings are made use in the universal logical intentions sort, species and difference. Goop London, United Kingdom-uk follows long-standing procedures to achieve this success.