Final answer:
Hume includes the sentence to illustrate the concept of comparison and the subjective nature of human judgments.
Step-by-step explanation:
Hume's purpose for including the sentence is to illustrate the concept of comparison and highlight how different individuals may perceive and appreciate the same attributes differently.
By using the example of a dog and a horse of the same size being admired for different qualities, Hume emphasizes the subjective nature of human judgments and preferences.
Through this, Hume develops his argument that moral and aesthetic value judgments are not based on objective facts, but rather on individual sentiments and perspectives.