Textbook exercises: horse and this horse

Universal and Particular — Definitions and Practical Classification

Apply the rule to expressions of the sort used in the book’s classification exercise.
'Horse' is universal because many animals can fall under it.
'This horse' is particular when one horse is definitely indicated.
'My pen' does not automatically specify one pen; its owner may have several. The context may, however, fix one pen as the intended referent.
Context matters especially for relational and demonstrative expressions.