In my school time, we learn that tense are of three types 1. Present Tense 2. Past Tense and 3. Future Tense. but i have heard that there is no Future Tense. is it true that only Present and Future is there and no Future Tense?
So my question is Actually how many tense are there? and How do we define the word "tense"?
How do we differentiate between these type of tenses?
I'm sorry, but there is no simple answer to this question. "Tense" as a category of grammar certainly exists; but the number and range of tenses varies both from language to language, and according to the grammatical theory applied.
In English, for example, I think everybody agrees that there are at least two tenses, present and past (I go vs. I went); but beyond that there are different views, depending on how you analyse the grammar.
Traditional accounts of English talk about "progressive or continuous tenses" (I am going, I was going, I have been going), and "perfect tenses" (I have gone, I had gone); but some grammarians prefer to regard these as aspects rather than tenses. The fact that you can combine these reasonably freely (eg I will have been about to go) suggests that they are not the same sort of phenomenon as is "tense" in a language like Latin, which has a fixed range of endings available for a verb.
Traditional views of English talk about the "future tense", but some grammarians deny that there is such a thing in English: the form called the "future" (I will go) is mostly used for future meaning, but it has other uses, and there are other ways of expressing future meaning. And syntactically it is completely indistinguishable from modal forms such as I may go).
The range of tenses available varies widely between languages: many languages do not have a form which unambiguously distinguishes future time from possibility.
