Step 1: Understanding the Doctrine of Monads.
Leibniz's Doctrine of Monads posits that the universe consists of fundamental, indivisible substances called monads. Each monad uniquely mirrors the entire universe. The statement "Body is a plurality of simple forces" resonates with this concept, as each force or substance, akin to a monad, acts as a simple unit while contributing to complex interactions.
Step 2: Analyzing the Options.
- 1. Mind-Body dualism: Descartes' theory, distinguishing mind and body as separate substances. This does not align with the description of forces.- 2. Categorical Imperative: Kant's ethical principle concerning duty, unrelated to the nature of forces.- 3. Doctrine of Modes: Spinoza's concept of substance modifications, not directly about forces or bodies.- 4. Doctrine of Monads: This is accurate. Leibniz's Doctrine of Monads directly addresses the idea of simple substances or forces that constitute complex bodies.
Step 3: Conclusion. Option 4, the Doctrine of Monads, is the correct answer.
Final Answer: \[ \boxed{\text{The correct answer is 4. Doctrine of Monads.}} \]