  We introduce a novel parser based on a probabilistic version of a left-corner
parser. The left-corner strategy is attractive because rule probabilities can
be conditioned on both top-down goals and bottom-up derivations. We develop the
underlying theory and explain how a grammar can be induced from analyzed data.
We show that the left-corner approach provides an advantage over simple
top-down probabilistic context-free grammars in parsing the Wall Street Journal
using a grammar induced from the Penn Treebank. We also conclude that the Penn
Treebank provides a fairly weak testbed due to the flatness of its bracketings
and to the obvious overgeneration and undergeneration of its induced grammar.
