You probably think you are rational. Day to day, you try to 'make the best possible use of the information available to you,' as MIT philosopher Brian Hedden PhD '12 writes in his 2015 book, 'Reasons without Persons.' If you think you are rational because of how you plan for the future, and change your beliefs over time, however, Hedden will be skeptical. Circumstances change, and when using reason, he thinks, all that matters is the present. Thus, he also writes: 'The requirements of rationality should be impersonal, avoiding reference to the relation of personal identity over time.' This is what Hedden calls 'time-slice rationality,' the idea that in applying reason, we exist in little slivers of time and knowledge. There are not permanently reasonable people, just reasonable decisions. 'We are temporally extended people with hopefully long lifespans, but we're made up of lots of different time slices,' Hedden says. 'So there's me now, me yesterday, me next year. We should think...
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