 The idea that mental content is broad is the idea that it is not determined entirely by an individual’s intrinsic properties, but is determined in part by features of the individual’s environment. But if the content of my beliefs is not determined entirely by my internal states, what else could determine it? How could anything other than my intrinsic properties determine what I think and believe? The examples just discussed point to two different sorts of environmental factor. Putnam’s example of Oscar and his Twin Earth duplicate focuses on the contribution of the natural environment. The crucial idea here is that when we have thoughts or beliefs about natural kinds, we often do not know what the essential features of those kinds are, even though we assume that there are such essential features. In such cases, what we are thinking about depends not only on internally available factors, but also on facts about the physical, chemical, or biological makeup of the kinds we are thinking about. Burge’s arthritis example, by contrast, focuses on the contribution of the social environment. In our thoughts about many kinds of things, including natural kinds but also including kinds invented by humans, such as furniture or contracts, we assume that others may have more expertise than we do about what is and what is not included in the kind in question. Thus, what we are thinking about depends not only on our intrinsic properties, but also on expert opinion. We defer to the experts with regard to what exactly we are thinking about. For this reason, this sort of contribution of the social environment is sometimes referred to as “semantic deference.”