Full Idea
B-theorists regard tensed sentences as incomplete expressions, implicitly containing an unfilled argument-place for the time at which they are to be evaluated.
Gist of Idea
B-theorists say tensed sentences have an unfilled argument-place for a time
Source
Kit Fine (Necessity and Non-Existence [2005], 01)
Book Reference
Fine,Kit: 'Modality and Tense' [OUP 2005], p.322
A Reaction
To distinguish past from future it looks as if you would need two argument-places, not one. Then there are 'used to be' and 'had been' to evaluate.