Strictly speaking there are only two tenses, but the idea of tense is usually extended to include aspect and voice.
Tenses: Present, Past.
Aspects: Simple, Perfect, Progressive, Perfect Progressive
Voices: Active, Passive
Each tense can be expressed in all four aspect possibilities, so there
are 8 tenses, not considering voice. Each of these 8 can be
expressed in two voices, so the total number of tenses (so far) is 16.
If we add combinations with the modals (
will, would, can, could, ...),
the number of tenses increases considerably! Each modal can be
used with the 4 aspects and 2 voices. Typically only the modal
will is included in the count (I don't know why!
would
seems equally useful, for example, in indicating time relationships.),
so this adds 8 more tenses for a total of 24 tenses. If we extend
the count by including the 8 tenses which can be formed with
would, we have 32 tenses in all.
CJ