Step 1: Understanding the Context.
René Descartes, a key figure in modern philosophy, emphasized the concept of substance and extension. He famously said that "the existence of bodies presupposes extension," meaning that for something to exist as a physical body, it must have spatial extension (it occupies space). This idea is central to his materialist and dualist philosophy.
Step 2: Analyzing the Options.
- 1. Bacon: Francis Bacon was a philosopher and scientist known for his work on the scientific method, but he did not emphasize the concept of extension in the way Descartes did.
- 2. Descartes: This is correct. Descartes emphasized that for something to be a material body, it must have extension.
- 3. Leibniz: Leibniz had a different view on substance and extension, focusing more on monads and metaphysics.
- 4. Spinoza: Spinoza was a pantheist who believed that everything is part of one substance but did not make the same point about extension as Descartes.
Step 3: Conclusion.
The correct answer is 2. Descartes.
Final Answer:
\[
\boxed{\text{The correct answer is 2. Descartes.}}
\]