There exist classifications embracing a rich variety of tenses. Temporal relations are considered by some scholars to be more complex than merely the present, the past and the future. Otto Jespersen's classification is most peculiar. He distinguishes main or simple times (Present and Past), subordinate times which are points in time posterior or anterior to some other point ( in the present, in the past or in the future). This is a logical scheme( the before past time, the after past time, the before future time, the after future time), with no simple future (She gave birth to a son who was to cause her great anxiety ( the after past). He excluded the future on the ground that in English there are no grammatical means to express pure futurity, the "so called future" being modal.
The writer of a popular manual in practical grammar prof. Kaushanskaya distinguished 16 tenses. Her practical scheme of tenses is based on O. Jespersen's scheme and comprises Progressive tenses (continuous, long) and Perfect tenses. There are 4 Indefinite tenses, 4 Continuous tenses, 4 Perfect tenses and 4 Perfect Continuous tenses.
The classifications embracing 3 tenses were advanced by Profs. Smirnitsky, Ilyish, Khlebnikova, et al. These classifications are based on a three tenses oppositional approach. It is the Past, the Present and the Future ( a tertiary equipollent opposition: went::goes:shall/will go). In two-tense classifications we find The Past and the Present, or The Present and the Future ( a binary privative opposition). In some schemes the Present is treated as an abstraction which cannot be objectively established. Others treat the Present stretching limitlessly into the future and into the past (prospectively and retrospectively).
The Evolution of English Grammars | The Asymmetry of a Linguistic Sign | Transformational and Transformational Generative Grammar | Semantic Syntax | The Oppositional Method | The Distributional method | The Transformational Method | The Method of Deep and Surface Structures | The Componential Method | The Contextual Method |