Abstract
Languages that are classified as non-Sequence-of-Tense come in more than one variety : some of these languages allow a past tense in before -clauses while others do not. We propose that some languages have quantificational tenses, while others have pronominal tenses. The past tense in before -clauses is ill-formed in a language that has quantificational tenses, because the semantics of before is incompatible with existential quantification over times. A language with pronominal tenses does not have this problem. The pronominal/quantificational tense distinction interacts with the Sequence-of-Tense parameter, providing a general theory of possible and impossible languages.