What is the present progressive? It is a sentence form. Longman Dictionary of Comtemporary English explains it like this:
“You make the present progressive by using a form of the verb be in the present tense,
followed by the main verb with an ing ending, for example l am waiting, she is coming.”
Later in the same text, Talking about the present, Longman notes that:
“You use the present progressive to say that something is happening now, but will only continue for a limited period of time. Compare these pairs of sentences:
We live in France. (=”France” is our permanent home)
We’re living in France. (=”we” are living there for a limited period of time)
He cooks his own meals. (=”he” always does it)
He’s cooking his own meals. (=”he” does not usually do it)”
I take it that “He cooks his own meals.” means that he has always and will always cook his own meals. So the “always” stretches both back in time and forward in time.1
If so, then I disagree with it. I don’t think think there is any change in meaning by using the present progressive instead of the simple present. I have created an example that seems to show that there is no implication about an eternity by using the present progressive. Consider:
E1. He cooks his own meals now.
I have inserted the word “now” in the end of Longman’s example. When “now” is used like this it implies that there has been some change. If there has been some change, then the past has not always been the same. If the past has not always been the same, then the proposition (E1) does not imply that there has been change in the past. Thus, the proposition (E1) and, by extension, the propositions expressed by the sentences of the form that (E1) has does not imply there has never been change in the past.
Moreover, if the proposition (E1) did imply that there has been no change in the past, then the proposition (E1) would be a contradiction, but it isn’t. Thus, the proposition (E1) and, by extension, the propositions expressed by the sentences of the form that (E1) has does not imply there has never been change in the past.
Similar considerations seems to show that the proposition (E2) does not imply that there is something non-permanent about the situation. Consider this sentence:
E2. It has always been and will always be the case that he’s cooking his own meals.
If propositions expressed by sentences that has the present progressive form did imply that there is something non-permanent about the situation, then the proposition (E2) would be a contradiction, but it isn’t. Thus, propositions expressed by sentences that has the present progressive form does not imply that there is something non-permanent about the situation.
1That a proposition expressed by a sentence that contains “always” does not imply that the individuals mentioned in the proposition will continue to exist for an eternity, of course.