Many reference and education-oriented websites have multiple pages devoted to the rules of verb tenses in English grammar, including Grammarly.com, EnglishLeap.com and Perfect-English-Grammar.com. Websites such as Learn-English-Today.com and Englisch-Hilfen.de focus on helping students learn English as a second language, which includes teaching the rules of tenses in English grammar.
Verbs are action words, and the tense of a verb tells when the action takes place. At the most basic level, English verb tenses tell if an action happened in the past, what is happening in the present, or happens in the future.
However, simply knowing when the action takes place is not always enough. English grammar accounts for this by further subdividing the basic tenses into four more constructions known as the simple, the perfect, the continuous and the continuous perfect.
These sub-tenses function analogously in past, present and future. A verb in the simple present tense, for example, happens instantly, or else it happens regularly or continuously. The verb "to see," for instance, is rendered as "The cat sees" in the simple present tense.
The present perfect tense is for an action begun in the past that either still matters or is ongoing. The tense is formed by combining the present tense of "to have" with the past participle of the verb.
The present continuous tense, sometimes called the present progressive, is actions that are taking place even as they are being described. It is formed by combining the present tense of "to be" with the present participle of the verb. In this instance, "The cat is seeing."
The present continuous perfect, also known as the present perfect progressive, is for actions that started in the past and are still happening in the present. It is formed by combining the present tense of "to have" and "to be" with the present participle of the verb. For example, "The cat has been seeing."