Which word best describes a person who is hard and unyielding in their beliefs?

The best word to describe a person who is hard and unyielding in their beliefs is "peremptory." This term indicates an assertive, commanding, and often imperious attitude in the way someone expresses their views, suggesting that they are not open to consideration or debate. A peremptory individual firmly maintains their stance and expects compliance from others, which aligns well with the idea of being inflexible in one's beliefs.

In contrast, the other options do not fit the description as well. "Pernicious" refers to something harmful or destructive, typically in a gradual way, and does not specifically address a person's rigidity in beliefs. "Philosophical" suggests a calm acceptance of life's challenges and involves a reflective attitude, which is quite the opposite of being unyielding. Lastly, "perverse" implies a deliberate desire to behave in an unreasonable or contrary manner, but it does not necessarily imply an unwavering adherence to beliefs. Therefore, "peremptory" effectively captures the essence of someone who is hard and unyielding in their convictions.