Difference between son et sont
French words "son" and "sont" are grammar homophones ie they do not have the same function in the sentence.
- sont comes from verb être conjugated to the indicative present : ils sont.
- son is possessive adjective such as mon & ton (my & you).
The best way to do their distinction is to change the sentence to another tense such as imperfect. At imperfect, sont becomes étaient meanwhile son does not change.
You can also try to replace "son" by "mon".
- ils sont venus nous voir. (présent)
- ils étaient venus nous voir. (imparfait)
- il appelle son chien. (We can't replace "étaient" but we can it by "mon")
- il appelle mon chien.