 Externalism appears in two major forms. Content externalism is externalism about mental content—the content of mental states. It claims that the contents of at least some mental states are not solely determined by occurrences falling within the biological boundaries of that individual that has them. Since mental states that have content are typically individuated by that content, this entails that which mental states an individual has is not completely determined by occurrences falling within the biological boundaries of that individual. Vehicle externalism, more commonly known as the thesis of the extended mind, is externalism about the vehicles of mental content. According to the thesis of extended mind, the vehicles of mental content—roughly, the physical or computational bearers of this content—are not always determined or exhausted by things occurring inside the biological boundaries of the individual. Content externalism and extended mind are logically independent views, and it is not uncommon to find adherents of one view denying the other. These two forms of externalism diverge sharply not simply because they are externalism about different things—contents and vehicles, respectively—but also because they have different conceptions of this failure of determination. If mental contents are not determined solely by what is occurring inside the biological boundaries of an individual, this is quite different from the way in which the vehicles of content are not determined solely by what is occurring inside these boundaries. In other words, each form of externalism differs not only in what it claims to be external, but also in what it means by “external”.