 In the preceding section, we surveyed issues that face the philosopher attempting to work out the details of a causal theory of mental content. These issues are, therefore, one might say, internal to causal theories. In this section, however, we shall review some of the objections that have been brought forward to the very idea of a causal theory of mental content. As such, these objections might be construed as external to the project of developing a causal theory of mental content. Some of these are coeval with causal theories and have been addressed in the literature, but some are relatively recent and have not been discussed in the literature. The first objections, discussed in subsections 4.1–4.4, in one way or another push against the idea that all content could be explained by appeal to a causal theory, but leave open the possibility that one or another causal theory might provide sufficiency conditions for meaning. The last objections, those discussed in subsections 4.5–4.6 challenge the ability of causal theories to provide even sufficiency conditions for mental content.