You have a mind and you have a body. What’s the connection between the two? All of us are aware of our physical being—our bodies—and we also have an immediate experience of our mental states—our thoughts, emotions, and sensations—but figuring out the relation between these has not been easy.

The oldest and by far the most popular explanation of the relationship between mind and body is calledsubstance dualism．让我们从“实质”的概念开始，来解读这个术语。哲学家们对“物质”这个词的使用不同于它在日常演讲中的使用。In the vernacular, substances are stuff like toothpaste or olive oil, but in philosophical jargon, substances are justthings．你的左脚、海王星和唐纳德·特朗普的头发都是技术和哲学意义上的物质。

The term “dualism” refers tokinds的物质。如果你是一个物质二元论者，你会认为有两种东西。有物质的，也有非物质的。想象一下，你正在对整个宇宙中的一切进行盘点。你拿着一个剪贴板，上面有一张分成两栏的纸。第一列被标记为“物理”，第二列被标记为“非物理”。如果你是一个物质二元论者，你认为有些东西属于第一栏(例如，你的身体、海王星和特朗普的头发)，而其他东西属于第二栏(例如，上帝、灵魂和思想)。Alternatively, if you are aphysicalist——相信一切都是物理的人——那么你就会相信一切都属于第一列，而没有任何东西属于第二列(我们将在本博客的未来部分探讨物理主义)。

Of course, the part of your body that’s most relevant to this discussion is the squishy piece of matter that’s lodged between your ears—your brain. If you’re a substance dualist you believe that your mind and your brain are not the same thing. Your brain is a physical thing—to put it crudely, it’s a piece of meat—while your mind, the locus of your conscious experiences, isn’t a physical thing at all.

长期以来，物质二元论对如此多的人如此有吸引力，这是有充分理由的。对许多人(可能是大多数人)来说，这种观点显然是正确的。想想。你的身体有你的思想似乎没有的特征。这是显而易见的。它在空间中延伸。它有表面，质量和体积。你可以触摸它，称量它，测量它。但是你现在用来思考你的身体的思维似乎是完全不同的事情。

让别人衡量你的思想或衡量你的某个想法的大小不是很奇怪吗?出于以下几个原因，提出这样的请求会很奇怪。一是精神上的东西似乎没有重量和尺寸这样的属性。同样地，精神世界的事物似乎具有不属于物质世界的事物的特征。你可能会有一个非理性的想法，但如果你说你的前额叶皮层有一个非理性的电化学冲动，这似乎会非常奇怪。

Another reason why such questions seem odd has to do withaccess．你的身体和其中发生的一切(至少在原则上)是别人所知的。事实上，有时候别人比你更能了解你内心的想法。例如，医生可能会告诉你你的胰腺现在正在发生什么，即使你不知道那里正在发生什么。

But we seem to be hooked up to our own minds in a special way. We seem to have direct and privileged access to our own mental life—our thoughts, fantasies, feelings and memories. And this realm is radically private and inaccessible to others, unless we chose to communicate our mental states to them.

These points about the difference between mental and physical states easily lead to dualistic conclusions. Here’s how the reasoning goes. If your mind has characteristics that your body doesn’t have, and vice versa, then your mind must be something separate and distinct from your body—hence, substance dualism must be true.

This pattern of reasoning can be formulated more sharply by drawing on a handy philosophical principle that’s known as “Leibniz’ Law,” which is named after the 17th to 18th century philosopher-mathematician-physicist and all-round genius Gottfried Wilhelm Leibniz who first formulated it. Leibniz Law is all about the conditions under which we can say two or more things (or, more accurately, what seems like two or more things) are identical.

When philosophers talk about two things being identical, they don’t usually mean “identical” in the sense that identical twins are identical. Identical twins arequalitativelyidentical, which means that they are so similar to each other that it’s hard to tell them apart. But philosophers are usually more concerned with what’s callednumericalidentity. To say that two things are numerically identical is to say that they are really the very same thing. Bruce Wayne and Batman are numerically identical becausethey’re the very same guy．

根据莱布尼茨定律，只有当两个事物具有完全相同的性质时，它们在数值上才相同。所以布鲁斯·韦恩之所以和蝙蝠侠一模一样是因为布鲁斯和蝙蝠侠有完全相同的特征。Everything that’s true of one is true of the other, and vice versa, because BatmanisBruce Wayne.

我的学生经常对莱布尼茨定律的标准描述感到困惑，因为两件事实际上是一件事的想法是没有意义的。他们是对的。Itisnonsensical to say that two things are really one thing. So let’s express Leibniz’ Law in a different way—one that focuses on names for things rather than the things themselves. Two names (for example, “Batman” and “Bruce Wayne”) are names for the very same thing only if the things that they name have exactly the same properties. Batman equals Bruce Wayne because the name “Batman” names a person who has precisely the same characteristics as the person named “Bruce Wayne” has. If Bruce is in Gotham City then it would be impossible for Batman to be anywhere else, and if Batman is fighting crime at 4:30 in the afternoon on Tuesday, then it would be impossible for Bruce not to be fighting crime at that moment.

现在我们可以回到物质二元论的问题上来。如果精神状态与大脑状态具有不同的属性是真的，而且我们有特权进入我们的思想而不是我们的身体，那么看起来莱布尼茨定律告诉我们，我们的思想和我们的身体在数字上并不相同。由此看来，我们是由两种不同物质的化合物组成的。我们是与非物质心灵相连的物质身体。

This seems like a satisfying conclusion, but is it true? Anyone that advocates substance dualism owes us an explanation of how it works. As we’ll see inthe next installment, that’s where the trouble with dualism begins.