In English grammar, the term "tense" traditionally refers to any conjugated form expressing grammatical tense, aspect, or mood. The large number of different composite verb forms means that English has the richest and subtlest system of tense and aspect of any Germanic language. This can be confusing for foreign learners; however, the English system can be presented systematically by noting that each of the temporal spheres (past, present, future) distinguishes simple forms from progressive (continuous), perfect, or both.
Sentences can be active or passive. Therefore, tenses also have "active forms" and "passive forms".
This table, of course, omits a number of forms which can be regarded as additional to the basic system: