Full Idea
The A-series puts events into past, present and future. The B-series puts events into a series based on relationships of 'before' and 'after'. McTaggart said the A-series was contradictory, and the B-series failed to cope with essential features of time.
Gist of Idea
A-series uses past, present and future; B-series uses 'before' and 'after'
Source
report of J.M.E. McTaggart (The Nature of Existence vol.2 [1927]) by Rod Girle - Modal Logics and Philosophy 8.10
Book Reference
Girle,Rod: 'Modal Logics and Philosophy' [Acumen 2000], p.137
A Reaction
The A-series is indexical.