take in two inches vs. shorten sth by two inches


I have some questions on the preposition “by”.

(1) I want the waist taken in two inches.
(2) Shorten the sleeves by two inches.

Shorten has the same meaning as take in. Then, why isn’t “by” used in (1)? I mean, shouldn’t it be “I want the wast taken in by two inches.”? So, my questions are:

a) Why is “by” used in (2) while it is not used in (1)?
b) If I put “by” before “two” in (1), would it be wrong?
c) When is the “by” used?

Thank you for your answers in advance,


‘Shorten’ is used to indicate reduction in length and we would use ‘by’ to indicate the amount. It could also be used in the same way with ‘reduce’ as in: Inflation has been reduced by 1%.

‘Take in’ is used not so much for length as for circumference/width and is usually followed without an additional preposition when talking of the mount. I suppose that ‘in’ is sufficient on its own.