  (Abridged) We consider the scientific case for a large aperture (10-12m
class) optical spectroscopic survey telescope with a field of view comparable
to that of LSST. Such a facility could enable transformational progress in
several areas of astrophysics, and may constitute an unmatched capability for
decades. Deep imaging from LSST and Euclid will provide accurate photometry for
spectroscopic targets beyond the reach of 4m class instruments. Such a facility
would revolutionise our understanding of the assembly and enrichment history of
the Milky Way and the role of dark matter through chemo-dynamical studies of
tens of millions of stars in the Local Group. Emission and absorption line
spectroscopy of redshift z=2-5 galaxies can be used to directly chart the
evolution of the cosmic web and examine its connection with activity in
galaxies. The facility will also have synergistic impact, e.g. in following up
live and transpired transients found with LSST, as well as providing targets
and the local environmental conditions for follow-up studies with E-ELT and
future space missions. Although our study is exploratory, we highlight a
specific telescope design with a 5 square degree field of view and an
additional focus that could host a next-generation panoramic IFU. We discuss
some technical challenges and operational models and recommend a conceptual
design study aimed at completing a more rigorous science case in the context of
a costed technical design.
