Don't understand past tense used as present perfect in Japanese

Question

I'm reading a Japanese beginners book in which I have found a 'present perfect' sentence for the first time, but I don't understand it very well:

The sentence

見たことがある女の人がいます

according to my book, is translated as:

There is someone she has seen before

My understanding is that in Japanese there is no present perfect, past tense is used instead and whether or not it is present perfect is infered by the context (source: this).

I still don't understand very well the sentence parts:

• Where is the 'before' in that sentence?
• I don't see how is that inferred that that sentence is present perfect and not past perfect, that is: 'There is someone she saw'
• How is that it has two が? It's like it has two subjects.
• What does the aru do there?

Answer 1

There are several things going on in this sentence, so let's look at them one by one.

見たことがある女の人がいます

First, there's a relative clause:

見たことがある

and then there's the main clause:

女の人がいます

The main clause just says

There is a woman.

が here marks the subject of the main clause.

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Regarding the relative clause

見たことがある

This is a special construction, which works as follows:

<past tense verb>ことがある

which means

Someone has had the experience of doing verb

Put another way, it means

Someone has previously experienced doing verb

So, in this particular case we have

Someone has previously seen something

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If we put the relative clause together with the main clause, note that the relative clause modifies 女の人. So we have

There is a woman who someone has previously seen.

which then can be worked as

There is a woman who [I,she,he,they]'ve seen before.

The choice here between I, she, he, they, etc all depends on who's in the scope of conversation. Without further context, a native speaker would default to understanding this as I. But, your book perhaps has provided a context or assumes one, which is she (a she difference from this particular woman)

Answer 2

You can see ～たことがある as a fixed form meaning "To have done ~ before" (see here).

If you are interested in the structure, ある is the usual ある, meaning something exists; こと nominalizes the verb, something like "The fact of [doing verb]" in English, like 食べること, "The fact of eating": since が as subject marker have to follow a noun, you need something to make 見た a noun, and that's こと. So 見たこと is something like "The fact of having seen in the past" ("in the past" because the verb is in past form).

If you add がある, i.e. "exist", 見たことがある literally means "It exists the fact of having seen [something] in the past"; but that, in a less literal and awkward translation, means that in the past the subject saw the object - i.e., "I have already seen".

There are two が because the first is linked to こと (as subject of ある), while the second to 女の人 (as subject of います): there is one sentence with its subject - 見たことがある - modifying another sentence with its subject - 女の人がいます.