It is important to study the word of these early critics of literature precisely because they are foundational in terms of our understanding of literature today, and they are the giants on which later critics interacted with their own understanding of what makes literature so special and unique. It is impossible to study any tragedy, even modern day tragedies such as those by Arthur Miller, without grappling with Aristotle's original definition of tragedy, which he describes as follows:

Tragedy, then, is an imitation of an action that is serious, complete, and of a certain magnitude; in language embellished with each kind of artistic ornament, the several kinds being found in separate parts of the play; in the form of action, not of narrative; with incidents arousing pity and fear, wherewith to accomplish its katharsis of such emotions... 

It is vital to be able to understand the original Aristotelian definition of tragedy in order to be able to see how Miller has taken the form of tragedy and kept some elements whilst adding and changing others in order to highlight the plight of the modern man trapped in a capitalist system that seems to undermine him at every turn (as is the case with Death of a Salesman). In the same way, the early criticism of Plato and Longinus are crucial to our understanding of later criticism and our very conception of what literature and poetry is and what it does to us. For any student of literature, it is impossible to avoid the ideas and theories that these writers penned completely, and even if their works are never actually read in the original, it is clear that they will be encountered in some way in order to heighten the understanding of literature and how it has changed and developed over the years.