The science case for an ELT covers a very wide range of topics from the study of exo-planets to fundamental parameters of the Universe. Here the case is summarised, and areas where an Antarctic site would provide advantages or limitations are considered. Simple scaling arguments are used to suggest that a “Moderately Extremely Large Telescope” (or “MELT”) of order 15–20 m diameter in Antarctica would be capable of carrying out some (but not all) of the observations currently envisaged for a $\sim $ 40 m class ELT at a temperate site. It is suggested that any such Antarctic telescope should be dedicated to a small number of specific science goals, chosen to complement ELTs at temperate sites.