Please explain the difference between metaphysical possibility and logical possibility

## Understanding the Distinction **Logical possibility** is the broadest category of what can be conceived without a formal contradiction. A scenario is logically possible if and only if its description does not violate the fundamental laws of logic, such as the law of non-contradiction ($A$ and not-$A$ cannot both be true). For example, a talking donkey is logically possible because the concept of a donkey and the concept of speech can be combined without generating a logical contradiction. **Metaphysical possibility**, by contrast, is constrained by the fundamental nature of reality, or what *could* exist given the actual laws and structures of the universe. While a logical possibility only requires freedom from contradiction, a metaphysical possibility requires compatibility with the essential properties of things. For instance, many philosophers argue that while it is logically possible for water to be composed of something other than $H_2O$ (since "water is not $H_2O$" contains no internal contradiction), it is metaphysically impossible because being $H_2O$ is the essential, defining nature of water. ## A Tangible Illustration Consider the proposition, "Gold can exist without having atomic number 79." From a purely logical standpoint, this is entirely possible. The sentence uses distinct concepts—the metal gold and an atomic number—that can be rearranged without breaking the rules of logic. However, contemporary metaphysicians often argue that this is **metaphysically impossible**. Under modern chemistry, having atomic number 79 is not merely a common feature of gold; it is the underlying essence that makes gold what it is. To strip gold of its atomic number is, in the metaphysical view, to strip away the very thing that constitutes it, making the scenario impossible in reality regardless of our ability to imagine it. ## State of Knowledge and Limitations The distinction between these two forms of possibility is a cornerstone of modern analytic philosophy, particularly modal epistemology (the study of how we know what is possible or necessary). It is well-established in philosophical semantics that logical space is wider than metaphysical space: everything that is metaphysically possible is also logically possible, but not vice versa. However, the boundaries of metaphysical possibility remain deeply contested. Unlike logical possibility, which relies on formal rules, metaphysical possibility often depends on controversial assumptions about "essences" and whether things have necessary properties independent of our language and concepts. Skeptics argue that metaphysical necessity is merely disguised linguistic convention or a projection of our current scientific theories rather than a deep feature of reality. ## Follow-up questions 1. How do different philosophical accounts of "essence" determine whether a scenario counts as metaphysically possible? 2. If water is necessarily $H_2O$, how should we assess historical scenarios where people drank water without knowing its chemical structure? 3. What are the strongest objections from empiricist philosophers who reject the idea that we can discover metaphysical necessities through pure reason?