 The third and final metaphysical issue that we will discuss in the context of time perception concerns causal asymmetry. The account of our sense of being located at a time which we considered under  Past, present and the passage of time  rested on the assumption that causation is asymmetric. Later events, it was suggested, cannot affect earlier ones, as a matter of mind-independent fact, and this is why we do not perceive the future, only the past. But attempts to explain the basis of causal asymmetry, in terms for example of counterfactual dependence, or in probabilistic terms, are notoriously problematic. One moral we might draw from the difficulties of reducing causal asymmetry to other asymmetries is that causal asymmetry is primitive, and so irreducible. Another is that that the search for a mind-independent account is mistaken. Perhaps causation in intrinsically symmetric, but some feature of our psychological constitution and relation to the world makes causation appear asymmetric. This causal perspectivalism is the line taken by Huw Price (1996). That causal asymmetry should be explained in part by our psychological constitution, in a way analogous to our understanding of secondary qualities such as colour, is a radical reversal of our ordinary assumptions, but then our ordinary understanding of a number of apparently objective features of the world—tense, absolute simultaneity—have met with similarly radical challenges. Now, if causal asymmetry is mind-dependent in this way, then we cannot appeal to it in accounting for our experience of temporal asymmetry—the difference between past and future.