1. ~とは (Means... / Is defined as...)
Meaning: Used to define or explain the nature or meaning of a thing, concept, or term.
✓ It is relatively formal and more written in tone than というのは.
✓ In definitions, the following clause often uses forms such as 〜だ、〜である、〜という意味である、〜のことである.
✓ It can also appear in questions such as 〜とは何か / 〜とはどういう意味か to ask what something is or what it means.
2. ~といえば (Speaking of... / Now that you mention it...)
This sentence pattern has two completely different uses depending on the context.
✓ From a given topic, it evokes or reminds one of another related story. (Speaking of this... it reminds me of that issue...).
✓ Used to accept or acknowledge someone else's viewpoint or the fact in the preceding clause, but the real (more important) point being made lies in the following clause. (It is true that..., but...).
B「そのようですね。安くなるといえば、飛行機のチケットが安く買えそうなんで、来月旅行しようと思っているんです。」
3. ~というと / ~といえば / ~といったら (Speaking of... / When you mention...)
Meaning: When a topic is mentioned, the speaker gives a typical association or something that comes to mind; というと / っていうと can also be used to confirm what was just said.
✓ In the associative use, the following clause gives an image, thing, or characteristic linked to the topic.
✓ It does not have to be the single “most representative” feature; it may simply be what the speaker associates with it.
✓ In the confirmation use, というと / っていうと is close to “when you say..., do you mean...?”
B「トップっていうと、去年オープンしたイタリアンレストランのことですよね。」
B「えっ。辞めるというと、もう来ないということですか。」
4. ~(のこと)となると (When it comes to...)
Meaning: Whenever a certain topic is brought up, the person's attitude changes unusually.
✓ The second clause implies an unexpected change in attitude, quite different from their usual behavior whenever that topic is touched upon (such as talking endlessly, acting like an expert...).
5. ~といったら (Speaking of... / When it comes to...)
Meaning: Emphasizes that the degree is much greater than usual when bringing up a certain topic.
✓ The second clause expresses an extraordinary level, showing astonishment or surprise to the extent that it cannot be described.
✓ In some cases, the sentence is cut off at といったら..., and the rest is completely omitted, yet the listener can still understand the implied degree.