A Philosophically Inexpensive Introduction to Twin-Earth
Frances, Bryan, A Philosophically Inexpensive Introduction to Twin-Earth.
孪生地球讨论这一个命题：Physical duplicates can have different thoughts. 张三及其复制品张3可以拥有不同的观念。【再通俗一些，即，张三及其克隆人张3，二人的物理身体一样，但是这并不意味着二人的观念一样。】【这种解读，是从身心关系的视角来看孪生地球】【孪生地球其实就是可能世界possible world的一种说法】
作者在该文分析了普特南的孪生地球的逻辑论证结构。并在最后提出六个问题并尝试解答。
在第二个问题中，作者提到了一些概念：
我们现代科学给我们的一个直觉是brain states fix or determine mental states.
依据这个直觉，我们有supervenience随附性：mental states supervene on brain states.
wide (or extrinsic) mental states：若除了我宇宙中没有其他东西，我将不会拥有这些状态。
narrow (or intrinsic) mental states：若宇宙中只有我，我仍然会拥有这些状态。
作者最后指出，反随附并不意味着外在。换言之，以下的推论是错误的：
（1）If anti-supervenient then wide; 或它的逻辑等价式：
（2）If narrow then supervenient
第三个问题中，作者指出以下两个逻辑关系是真的：
supervenient --> narrow 随附蕴涵内在
wide --> non-supervenient 外在蕴涵非随附
反之则不成立。（即，不是充分必要条件）
第四个问题，作者指出，
Anti-individualism focuses on supervenience: it says that beliefs are anti-supervenient. Externalism is a different claim: it says beliefs are wide. 反个体主义关心随附性；外在主义关心外在性。
AI:
The article "A Philosophically Inexpensive Introduction to Twin-Earth" by Bryan Frances presents a variant of the Twin-Earth thought experiment, designed to address key debates in philosophy of language and mind, particularly focusing on externalism and anti-individualism. The essay explores how meanings and beliefs can differ across possible worlds despite physical identity. It uses the example of two similar fish species, "walleye" and "sauger," to illustrate how word meanings and beliefs can shift when the meanings of these words are switched in an imaginary world.
Key takeaways include:
1. **Linguistic Anti-Individualism**: This argues that the meanings of words aren't determined solely by what's in our heads but also by external factors. Bryan can be physically identical in two worlds but still express different meanings due to these external factors.
2. **Mental Anti-Individualism**: Bryan can have different beliefs in two worlds while being physically identical. This shows that beliefs aren't solely determined by internal, physical states.
The article continues with technical discussions on **narrow content** (thoughts that are internal and don’t depend on the external environment), concepts of **intensions and extensions**, and an analysis of Putnam's famous Twin-Earth argument about how content isn't just "in the head."
### The Last Section's Questions and Answers:
1. **Extensions and Intensions**: Extensions refer to the things a word applies to, while intensions are the meanings behind those words. The debate arises when considering whether intensions always determine extensions and vice versa. In some cases, different intensions (like "creature with a heart" vs. "creature with a kidney") may pick out the same extensions (the same set of animals).
2. **Narrow, Wide, and Supervenient States**: Narrow states are mental states that do not depend on the external world, while wide states do. Supervenience refers to mental states being determined by physical states. The text explores how narrow and wide states relate to supervenience, showing that narrow states might not always supervene on physical states.
3. **Externalism vs. Anti-Individualism**: Externalism posits that the content of beliefs is influenced by external factors, not just what's inside a person’s mind. Anti-individualism suggests that even if two people are physically identical, their beliefs can differ due to their external environments.
4. **Is Meaning in the Head?**: A significant question raised is whether meaning is purely a mental phenomenon or whether external factors play a crucial role in determining meaning. Externalism argues that meanings are not just "in the head" but are also shaped by external contexts and the way words are used in the world.
The answers aim to clarify these complex philosophical concepts while showing how they relate to the original Twin-Earth experiment and contemporary debates.