Pathos, ethos and logos are the three pillars of persuasion. It is sometimes difficult to write a persuasive essay without using those.
Pathos is the appeal to emotions, ethos is the appeal to credibility or authority (do you believe the writer's or speaker's claims?) and logos is the appeal to logic, usually in the form of facts or statistics.
Although Animal Farm is a fable about animals, it uses all three forms.