In Japanese, if you want to describe something or someone that is performing an action, one of the ways you can do this is through a relative clause. A relative clause is when two phrases are joined into one sentence, rather than two individual sentences. The た (plain-past), or ている (continuous) form of verbs are usually used.

る-Verbs and う-Verbs follow their regular conjugation rules when making a relative clause. In the first example, we can see that 'Takashi-san is a man that lived in Tokyo', is one sentence, rather than 'Takashi-san is a man. He lived in Tokyo'. In English, words like 'that', and 'which' are used to create a relative clause. However, seeing as though these words do not exist in Japanese, the first phrase is simply attached to the noun.

Caution

The ます (polite) forms of verbs may not be used when making a relative clause.

In this expression, がある has the role of describing the noun that follows it. The description that it is giving is '(A) がある (B)' = '(B) has/with (A)'. This type of phrase is called a relative clause (something that describes a noun), and behaves similarly to an adjective.

In English, a relative clause would require a pronoun such as 'who' 誰(だれ), 'which' どれ, 'that' それ・あれ, 'where' どこ. However, these types of words are not required in Japanese, and the noun will follow がある directly.

Caution

In a relative clause, because (A) is describing (B), (B) will be considered the 'main topic/subject'. This means that は will generally not be used in place of が. However, の can be used instead of が, as showing a relationship between (A) and (B) is one of the main functions of の.

In some cases, the particle の can be used in place of が to mark a subject. This happens in subordinate clauses that describe or modify a noun, where the subject marked by の is not the main subject of the sentence.

There are two main reasons why someone may choose to use の instead of が.

First, if there is already another が, marking the main subject of the sentence, then it normally sounds more natural to not repeat が twice in the same sentence.

Second, が can put emphasis on the thing that it marks, delineating it specifically as new or noteworthy. Using の instead of が sounds less strong, so something else in the sentence can be emphasized.

Caution

が is not swapped for の if the clause contains an object marked by を. In such cases, の will be interpreted as the possessive particle, thus changing the meaning entirely.