Philosophy of modern astronomy & cosmology is a relatively novel field. Its main research centers are/ have been in the UK and in North America, with a strong focus on the epistemological aspects of astronomy and cosmology. The research programme that I am continuing to develop aims a) to make the EU a strong center for philosophy of astronomy and cosmology (PAC), and b) to ensure a well-rounded approach to PAC, by including metaphysical and semantical research questions. In particular, the astronomical and cosmological context is well-suited to question the tenability of the most primary ontological dichotomy, since Newton’s time dogmatically held to be sacrosanct, namely that every entity in our universe must be either spacetime (the container) or matter (the contained); it cannot be a bit of both, it cannot be neither. Preliminary work has focused on the case study of dark matter. Future work will focus on black holes, inflation and spin-2 gravity. This Marie Curie project focuses on the case study of dark energy, the mysterious ‘stuff’ held responsible for the accelerated expansion of our universe. The main hypothesis of the PhilDarkEnergy project is that dark energy cannot be neatly categorised as either pure container or pure contained. The dark energy case is particularly interesting since it brings to the fore a third category, that of a constant of nature, as the most simple and popular interpretation of dark energy is in the form of a cosmological constant.