の

1. 1Links a person or thing to something belonging to or associated with it.Ex. 1
2. 2Links a noun to another noun to describe an attribute such as its material.Ex. 2
3. 3Turns a verb or adjective phrase into a noun-like expression.

Neutral in register, の commonly expresses possession or attributes within a noun phrase. It can also stand in for an understood noun or turn a verb or adjective phrase into a noun-like expression.

• がN5「が」 marks the subject or appears at the end of a clause to mean 'but' (contrast), while 「の」 connects nouns to show possession/modification or nominalizes verbs and adjectives. They generally cannot be swapped, except that in relative clauses the subject can take 「の」 instead of 「が」, as in 「私が／の書いた本」.
• のが好きN5「のが好き」 uses 「の」 to nominalize a verb phrase, meaning 'like doing something', as in 「読むのが好き」. Here 「の」 is not the usage that links two nouns to show possession.
• ことN3「こと」 corresponds only to the nominalizing sense of 「の」, not to possession or other relations; it feels more abstract and formal, and in predicate sentences like 「趣味は〜ことです」 as well as in 「ことができる」 and 「ことがある」, only 「こと」 can be used.
• ということN4Only the nominalizing usage is similar: 「の」 points to a concrete action perceived on the spot, as in 「歌っているのを聞いた」, while 「ということ」 refers to a fact or what one has heard or learned. After na-adjectives, 「の」 takes 「な」 while 「ということ」 takes 「だ」.
• はN5「の」 combines two nouns into one noun phrase, as in 「私の本」, whereas 「は」 lifts a noun out as the topic of the whole sentence and follows it with an explanation, as in 「私は学生です」. Their functions differ and they cannot be interchanged.

は marks a topic and が marks a subject, while の links nouns or makes a phrase noun-like; のが好き uses that noun-like phrase with が好き to express liking. こと also nominalizes, while ということ presents a clause as stated information.