zurpk wrote:
I have been thinking about this point for the last four days.
I am thinking about this point from the last four days.
"I have been thinking about this point for the last four days."
This sentence is correct. "I have been" is past tense, and "the last four days" is past tense.
"I am thinking about this point from the last four days."
This sentence is incorrect. First of all, "I am thinking about" is present tense which conflicts with "the last four days."
Now, can we say, "I have been thinking about this from the last four days" -- The answer is no. As Arjun briefly explained, "from" is a starting point. If you say "from" then you are referring to one point in time, which is four days ago. But if you are continually thinking about it, then there is no starting point. That means, you cannot use "from"
Hope this clarifies your question.