Aristotle believes that all men have a desire to know and that it is our telos (the goal towards which something tends) to know.  Aristotle recognizes that all previous attempts to discuss “being qua being” have failed because they did not establish or use proper methodology in addressing the questio (What is being qua being?).  In Metaphyics, he hopes to establish such a methodology and even answer the question.  He wants to do this because he desires to know the highest knowledge (being qua being).  It is the highest because it is the first; if he can establish it as a science all other sciences must rest upon it rather than assumptions about it.

As with all other sciences, this “first science” must have an arche upon which to rest.  That is the principle of non-contradiction.  More or less the principle of non-contradiction states that something can not be and not be at the same time (What is white can not also be not white). 

There are many kinds/types of be-ing but since we are looking for being as be-ing we want to look for what they share in common; the primary being(s).  This is all tied to reality through the logos.  A thing is the way it is because of how we grasp it through the logos (how we define it).  Aristotle are searching out the primary being(s) in hopes that it will help him to better understand being qua being. 

A thing has many attributes and there are two kinds of attributes: accidental and essential/neccesary.  Accidental is something that is not always or usually so.  Essential attributes are things which are always or usually so.