Step 1: Understanding Berkeley’s Idealism.
George Berkeley, an Irish philosopher, famously asserted that "To be is to be perceived," encapsulating his idealist philosophy. According to Berkeley, material objects do not exist independently of the mind. Instead, their existence is contingent upon being perceived by a mind (either human or divine).
Step 2: Analyzing the Options.
- 1. Locke: Locke believed in empiricism and the existence of primary and secondary qualities of matter but did not endorse Berkeley’s idea of reality being dependent on perception.
- 2. Kant: Kant argued that while we can never know the thing-in-itself (noumenon), he did not claim that existence is equivalent to being perceived.
- 3. Berkeley: This is correct. Berkeley’s idealism asserts that things exist only insofar as they are perceived.
- 4. Hume: Hume, a skeptic, questioned the nature of causality and perception but did not reduce existence to perception in the way Berkeley did.
Step 3: Conclusion.
The correct answer is 3. Berkeley.
Final Answer:
\[
\boxed{\text{The correct answer is 3. Berkeley.}}
\]