As he has said, these are not "iron clad categories which do not overlap" (Kinneavy 297).
Yet, issue may arise from the classifications that Kinneavy cites from other authors, not namely their monikers, or the categories that that have invented, but the pyramid/ladder/hierarchy to which a subtle importance has been authorized to whichever is at the top; usually, some form of empiricism, or fact based approach.
Again, there is nothing wrong with the classifications themselves, but what may become problematic lies in their practice, for practice does not beget true, or in Kinneavy's term "Pure" (Kinneavy 301) discourse (although, in the context of his argument, he would wish us to realize these terms as existing in a "scientific vacuum" (Kinneavy 297)). There is no medium by which information is simply transmitted without the context of other influences, in his terms, the expressive, the persuasive, and the literary. This is where his diagram does him a slight injustice. The focus and breakdown of the communication process is more than adequate, representative and enforced by the corners (encoder, decoder, reality) and containing the signal (Kinneavy 302), yet as even he points out, there are intersections and influence that 2 dimensions can not describe, such as Kinneavy's notation of expressive situations (such as the conversation) that also might carry strong undertones of persuasion (focus on decoder) and reference (focus on what is fact, or agreed reality).
In class, it was thought that a 3d model would fix this, and rightly so. These grey areas would be easily rectified by the positioning of their aim in space according to how they manipulate Kinneavy's basic aims.
But I would like to propose to go one step further.
To create a 3d model would, in my mind, no doubt bear further implication in conversation with theorists past; for example, the position of a particular discourse within this 3d model would also represent the manipulation of discourse "differands" (Derrida). In a loose generalization, it would set standards for what could be considered particular discourse, not by singular aim, but by composition of multiple aims, and the way that they either negate, support, or in better terms,
Secondly, not only would these dots represents a more nuanced understanding of mixed aim, but this new view and location, would allow for what Longinus referred to as the "sublime" nature of discourse. Instead of the compartments and angles that categories tend to impose on the mental process, we would, after study of course, be able to view works as organic wholes, not by the breakdown of individual elements, by the total raw power and effect exerted to the combined and complete and singular utterance, which would be what we call discourse. It would instead be the ability (which we already all have but through schooling gets somewhat obscured) to look at mountain in conjunction with rivers and hills and sky, and call it "countryside" and implicitly know, by location, time and place, the elements to which sublimity is lent.