Why aren't the 'progressive' verbal constructions (such as 'I am talking') regarded as tenses in traditional grammar?
"There is no consensus, not even among linguists, about what constitutes a tense."--yeah, okay, fair enough, but that is hardly an answer.
"I have worked"--a tense, apparently. "I am working"--not a tense, apparently. There is no aspect of this that I understand. Why is the line drawn here?
Okay, further edit for clarification--I am referring specifically to the McGraw-Hill Handbook of English Grammar and Usage, which describes six tenses--3 simple and 3 perfect. I can see no justification whatsoever for this classification.
Furthermore, I can see no practical use for the concept of tense, in any of its varied applications. So why even bother with it? (In English, at least. I'm willing to accept that it may be a very useful concept in other languages.)