Difference between on and on n'
This time, we are on the border of a homophone because we have on one side a word "on" and on the other two words "on n'" which are the contraction of "on ne". But this doesn't take anything away from the difficulty of writing them.
- on is a third person singular pronoun. It is used to designate a subject of indefinite number, replacing a passive form. Familiar uses also put it in place of us or other personal pronouns.
- on n' is, as for him, always the same personal pronoun but with this time the mark of negation with the "n'".
The simplest way to distinguish them is to replace the "on" with "nous" or another person and see whether the mark of negation remains or not.
Another way is to spot a mark of negation such as not, never, hardly, more etc. As soon as you find this negation mark, there is a good chance that there is an "n'".
You can also try to replace the verb with another verb that does not begin with a or e. In this case, the n' becomes ne and one can clearly hear the mark of the negation.
- on entend du bruit
==> nous entendons du bruit
- on n'est guère optimiste
==> il n'est guère optimiste
- on n'aime pas la soupe
==> on ne mange pas la soupe