What does this sentence mean: "It is easier to make a 3-inch mirror and then to make a 6-inch mirror than to make a 6-inch mirror from scratch"?

It seems to say that A is easier than B, with A being "make a 3-inch mirror and then to make a 6-inch mirror", and B being "make a 6-inch mirror from scratch". But why that makes sense?

  • 2
    You've gained experience with a simpler but very similar task. Jul 8, 2017 at 23:30
  • Would you elaborate? I am still confused.
    – zell
    Jul 9, 2017 at 0:03
  • Your question reads "it is" and should read "is it."
    – MAA
    Jul 9, 2017 at 0:37
  • Oh, I see the question mark is not part of the quotation :) nevermind
    – MAA
    Jul 9, 2017 at 0:38
  • It's what @EdwinAshworth said but I wanted to make sure you were clear why and also explain the meaning a littler further. It's saying that it's easier to get to the 6in if you already have a 3in because you only need to add 3in. It does not mean that it's "logically" simpler. Nothing at all to do with the logic of the scenario. It just means to say you should take small steps and learn by doing smaller things first. You have heard the phrase, "You have to learn to walk before you can run."? Same thing. It means to attempt small tasks before you tackle larger ones.
    – Kace36
    Jul 9, 2017 at 7:20

1 Answer 1


I don't know why they use mirrors for this example, but the concept of making a small model of something before making the full sized thing is common.

For example, this company is building a smaller demonstrator aircraft capable of supersonic flight, before they begin building the full size passenger airliner. The reason is that it will be less expensive to learn from their mistakes on the smaller version. This way, when they go to make the larger full size aircraft they have figured out all the technical issues of making it. I guess this is like making a little mirror before making a larger one.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.