My question is one I saw on a site it is.I want to know the difference between the sentences.

  1. By 2025, I think we will build a settlement on Mars.


  1. By 2025, I think we will have built a settlement on Mars.

Also can you please tell me the meaning of:

By 2025, I think we would have built a settlement on Mars.

  • Of course both could be better put "I think that..." to separate the present thinking from the future building—but phrasing such as that quoted is not uncommon. Jun 29, 2015 at 9:12

1 Answer 1


The first sentence uses a simple future. It means that by 2025, they begin to build, start to build a settlement. In the second sentence, however, a future perfect is used, meaning that by 2025, the process of building that settlement will have been completed.

So, simply put: In the first sentence, the settlement will not yet be there by 2025, but in the second sentence, the settlement will be completely finished and ready by 2025.

  • The only 'simple present' here is think, which is in both sentences. In traditional grammar will build is called 'simple future' and will have built is called 'future perfect'. And will build will usually be taken to signify completion; non-completion would be signified with a progressive future, we will be building. Jun 28, 2015 at 15:16
  • You are correct. I updated my answer accordingly.
    – Vlammuh
    Jun 28, 2015 at 15:19

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