The document discusses verb tenses and their classification. It describes how tenses can be categorized based on time frame into present, past and future tenses. Tenses can also be categorized based on aspect into simple, continuous, perfect and perfect continuous forms. There are 12 possible verb tenses in total. The document provides definitions and examples of each tense like the present indefinite tense expresses an unchanging present action while the past perfect continuous tense describes an ongoing past action that was interrupted.