1-The sun rises in the east.
2-He reached his office in time.
3-Will you help me?
Why are these tenses called Indefinite-past, present or future? Of course, they are also called simple but what is the reason of their being called indefinite?
Indefinite is not a tense as such, it's an aspect that corresponds in English to simple tenses. It's best understood when you compare it to the perfect (complete) and imperfect (incomplete) aspect. Perfect describes an action that is completed, imperfect an action that is in progress. Indefinite aspect is neither -- the completion or beginning of the action doesn't matter.
Aspects are much more important in some other languages (such as Russian) but not really in English.
Aspects is one way to consider English verbs. That is, aspects exist should one wish to look for them. I guess I have a Slavic perspective where aspect is extremely important. English tenses can be learned very successfully without the word aspect being uttered. I consider it more important to learn how the tenses relate to each other, that is their sequence. Of course aspect enters into it, but it doesn't need to be discussed as such.
I learned on another forum that this topic can start a lot of fighting and hostility, especially when one starts discussing present perfect. So, let's leave it at this.![]()