I have a PhD in theoretical physics and am coming to the end of my first (one-year) postdoc. However, I have recently discovered that I am far more interested in the philosophy of science than my current work. I read papers in that field and I think I have a lot to contribute, but I don't know how realistic it is to try to publish or apply for academic jobs without a humanities PhD. I probably could afford to do a part-time PhD whilst working in physics but that would be another 6-7 years which doesn't seem realistic. Another option is to apply for a fellowship in the philosophy of science and hope for the best, but I suspect such funding would be extremely competitive. Is it possible to switch careers at postdoc stage? The actual subject of my research wouldn't be so different but there's a huge conceptual shift between science and humanities.