Translation guide
The English word "itself" is used for emphasis or to refer back to a thing. Japanese often omits the equivalent word, uses specific structures for emphasis, or relies on context. Direct translation is rarely natural.
The problem itself is easy.
The idea itself isn't bad.
そのもの (そのもの) attached to a noun also means 'itself', often with a nuance of 'the very thing' or 'in and of itself'.
Life itself is a journey.
In many cases, Japanese simply omits the equivalent of 'itself' because the context makes the emphasis clear. Adding 自体 or そのもの can sound overly emphatic.
This machine operates by itself.
To indicate that something does something without help or is alone.
Used for inanimate objects or things that happen spontaneously, meaning 'by itself' or 'automatically'.
The door opened by itself.
Means 'automatically', often used for machines or systems.
This machine operates by itself.
Means 'independently' or 'alone', more formal or technical.
The device functions by itself.
To say that something has a certain quality considered on its own, without external factors.
English often uses 'itself' for emphasis where Japanese uses context or a different structure. Directly translating 'itself' as 自分 (じぶん) is incorrect for things; 自分 is for people.
If the sentence is clear without 自体 or そのもの, it's often more natural to leave it out. Overusing these can sound like you're translating from English.