のは・のがVerb nominalizer, The one who..., That which...

The particle の often shows possession, like the English ''s' (e.g., ケンジの本 means 'Kenji's book'). It can also connect two nouns, as in 日本人の学生 ('a student who is Japanese'). In contrast, は marks the topic of the sentence. Unlike の, it doesn't show possession — it introduces what the rest of the sentence will describe or explain.

の shows possession, like the English 's' (e.g., ケンジの本 = 'Kenji's book'). が marks the subject of a clause, often the doer of an action or the one with a certain trait. In modifying phrases, の and が are sometimes interchangeable without changing the meaning—for example, 先生が書いた本 and 先生の書いた本 both mean 'the book the teacher wrote.'

In the phrase AのB, の indicates a relationship between A and B, either possession (e.g., ジョンの本 = 'John's book') or description (e.g., 日本人の学生 = 'A Japanese student'). Particle + の is a variation where a phrase with a particle describes another noun (e.g., 先生からの手紙 = 'A letter from the teacher'). Note that particles like に, も, は, が, and を are typically not used in this construction.

Both こと and の turn verbs or adjectives into noun phrases. こと is used for intangible or conceptual ideas, while の is used for more tangible or physical concepts. For example, 走るのが好きです and 走ることが好きです both mean 'I like running,' with の feeling more physical and こと more conceptual. However, they aren't interchangeable in set phrases like ことができる or ことがある.

The particle の connects nouns to indicate possession or description. For example, 私の本 means 'my book.' When used with the pronoun の (meaning 'one'), the second の is dropped. For instance, to say 'It's mine,' you would say 私のです, not 私ののです.

Both of these patterns use の to turn a phrase into a noun. For example, the verb 走る ('to run') becomes 走るのが好き ('I like running') because the subject marker が must follow a noun. The Adjective + の(は) pattern works similarly, turning adjectives into noun phrases (e.g., 赤い ('red') becomes 赤いのはきれいです ('The red one is pretty')).