Which philosopher argued that the existence of forms is necessary to discuss general features like justice and beauty?

The philosopher who argued that the existence of forms is necessary to discuss general features like justice and beauty is actually Plato, although he is not listed among the provided choices. Plato's theory of forms posits that non-material abstract forms (or ideas) represent the most accurate reality and underpin our understanding of concepts such as justice, beauty, and goodness.

Brian Davies, while he has made contributions to philosophy and might discuss concepts related to forms in his work, is not the philosopher famously associated with the theory of forms in the same way that Plato is. Aristotle, on the other hand, critiqued and built upon Plato's ideas but did not maintain that forms exist in a separate realm; instead, he believed that forms are intrinsic to objects themselves.

In summary, the emphasis on the necessity of forms for discussing concepts like justice and beauty fundamentally belongs to Plato, which means that Brian Davies wouldn't be the most accurate choice, as he does not advocate for this specific idealist framework in relation to forms.