it·self 
/ɪtˈsɛlf/ pronoun
/ɪtˈsɛlf/ pronoun 1 : that same one: a — used as the object of a verb or preposition to refer to something that has already been mentioned ▪ The cat washed itself. ▪ History keeps repeating itself. ▪ The problem should work itself out. ▪ The chain folds back on itself. ▪ The restaurant has built quite a reputation for itself.
b — used for emphasis to refer to something that has already been mentioned ▪ I found the envelope, but the letter itself was missing. ▪ That itself was enough of an excuse. ▪ The city itself is fairly small. 2 — used after a noun to say that someone or something has a lot of a particular quality ▪ She was/seemed kindness itself. [=she was extremely kind] ▪ Your cake is perfection itself. [=your cake is perfect]
b — used for emphasis to refer to something that has already been mentioned ▪ I found the envelope, but the letter itself was missing. ▪ That itself was enough of an excuse. ▪ The city itself is fairly small.
by itself 1 : on its own : without being directly controlled by a person
▪ The computer shuts off by itself if you don't use it. ▪ The sprinkler will turn on by itself. [=automatically] 2 : with nothing nearby : alone
▪ The house stood by itself at the end of the street.
▪ The computer shuts off by itself if you don't use it. ▪ The sprinkler will turn on by itself. [=automatically]
▪ The house stood by itself at the end of the street.
in itself
: in its own nature : when considered as something separate from other things
▪ The idea was not in itself bad. ▪ This is not in itself a new idea. : without anything else added ▪ That's a story in itself. — see also an end in itself at 1end
▪ The idea was not in itself bad. ▪ This is not in itself a new idea. : without anything else added ▪ That's a story in itself. — see also an end in itself at 1end
