Final answer:
Thomas Hobbes claimed that in the state of nature, life was brutal and short. The concept that the world is inherently colorless or odorless aligns with empirical skepticism, not attributed to an individual. In Euthyphro, piety is one part of justice, with Socrates seeking to understand the other. Plato argues that true courage is knowing which fears are justified.
Step-by-step explanation:
A. The claim that in the state of nature, the life of man is solitary, poor, nasty, brutish, and short was made by Thomas Hobbes.
B. The argument that the world itself is colorless, odorless, silent and tasteless refers to the philosophy of empirical skepticism, suggesting that our perception of the world involves adding qualities that are not inherently present in the physical world itself.
C. In Euthyphro's dialogue, one part of justice is piety, which Euthyphro initially defines as what is pleasing to the gods, though Socrates challenges this definition. The other part of justice is not precisely defined in this dialogue, but Socrates seeks a clear definition of piety to understand its relation to justice.
D. The claim that true courage is knowing what to fear and what not to fear is attributed to Plato, specifically in the context of his dialogues involving Socrates. In 'The Republic', Socrates suggests that true courage is a quality of the spirited part of the soul and involves appropriate assessment of what should be feared.