So, I've gone through a good number of results that I got from BNCweb English language corpus, and can conclude that all these three tenses are used with "until now".

If we consider the following sentence: "Until now it has been thought that interferon can do little to prevent the initial entry of viruses into a cell.", why is the usage of the Present Perfect tense here is justified?

As, if I understand it correctly, at the time of the actual utterance, it is no longer thought that interferon can do little to prevent the initial entry of viruses into a cell. And, if I understand it correctly too, "until now" refers to the past. (Or is the word "now" means a more extended period of time?) Why is it not phrased as "Until now it was thought that interferon can do little to prevent the initial entry of viruses into a cell." or "Until now it had been thought that interferon can do little to prevent the initial entry of viruses into a cell."?

But let us consider a different example sentence, in which I think the usage is justified (I'll try to explain why I think so) : "Until now I have abstained from commenting on the possible effects of the Human Genome Project on society in future." I suppose this sentence is fine if the speaker is about to comment on those effects, and would not make any sense if any comments had been made by the time the sentence was uttered.

Another (and the last) example is: Until now we have assumed that banks decide for themselves upon the appropriate ratio in the light of their desire for profit and need for liquidity.

Perhaps it has something to do with the main verbs "think" and "assume"? Or am I missing something absolutely obvious here?

I am asking this because I keep finding a definition that the Present Perfect can be used for activity that lasted up until but not including the present, but in the examples above...the activity seems to have already ended.

I am very much sorry if I have asked too verbose a question, but I thought it would be helpful for me to provide some context sentences.

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    I think both examples use now to mean, not 'this exact moment', but 'now that [this change has happened]'. Your first example could be expressed as "Until [this discovery was made] it had been thought that interferon could do little..." Commented Oct 30, 2023 at 11:14
  • Where did you find the first quoted sentence? It's illogical rather than ungrammatical. It should be "it had been thought", because it is now no longer thought. Using "has been" implies it is still thought. Have you considered the possibility that it could just be a typo? The letters d and s are right next to each other on a keyboard after all.
    – Billy Kerr
    Commented Oct 30, 2023 at 11:28
  • You shouldn't necessarily assume that just because something does or doesn't appear in some corpus that it is correct or not. Human beings make mistakes, and errors often make it into published works.
    – Billy Kerr
    Commented Oct 30, 2023 at 11:40
  • @BillyKerr, not necessarily illogical… depending (as always!) on context. This kind of expression of temporal relationships is common in scholarly scientific writing. It’s as though within the presentation of a new result, the state of our collective knowledge is not altered by that presentation until the presentation has been completed. Call it a stylistic conceit if you like, but I prefer to see it as reflecting intellectual modesty: “It is not known whether X. Here’s a bunch of new information relevant to X,” even when, in fact, the new information all but settles that yes, indeed, X. Commented Oct 30, 2023 at 11:44
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    @BillyKerr I am thankful for all the suggestions! I have tried, in the meantime, to trace the source (with what limited information the corpus has on it), and here is what I have found so far: the source is most likely some periodical named "New Scientist", and the publication date is within the 1985-1993 range...not much, but it is at least something, I hope! Commented Oct 30, 2023 at 14:33

1 Answer 1


Why is the usage of the Present Perfect tense here justified?

If the sentence refers to a time in the past, you should use some version of a past tense: "Until last year, it (had been/was) thought that..."

However, what about "now"? It depends on how "now" is conceptualized. When referring to knowledge in the field of science, distributed across thousands of people, a change in perception is not instantaneous. Some will have adopted the new idea, while others haven't even heard about it yet. The period of time called "now" might be measured in years and is still occurring, as the idea about interferon propagates.

If it's still occurring (now), then you can't really use the past tense.

When an event happened in the past but is also still relevant at the moment, the Present Perfect fits very well. It seems to be the optimal choice.

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