打ち合わせる

That's a great question! While both relate to meetings, there's a key difference. 会議 (かいぎ) is a more general term for a formal meeting, often with a set agenda and a larger group. Think of it like a conference or a formal board meeting. 打ち合わせる (うちあわせる), on the other hand, usually refers to a more informal, preparatory meeting, often with a smaller group, to discuss and iron out details before a main event or decision. It's about 'coordinating' or 'pre-arranging' things. So, you might have an 打ち合わせ before a 会議.

Generally, 打ち合わせる is very much associated with business or project-related discussions. While you might informally use it with friends if you're planning something complex, it's not the most natural choice for casual social meetups. For personal plans, phrases like 話し合う (はなしあう), meaning 'to discuss,' or 相談する (そうだんする), meaning 'to consult/talk over,' are usually more appropriate.

To use 打ち合わせる, you usually need a subject (who is meeting) and often a topic or purpose. Here's a common pattern: [Subject] が [Topic] について打ち合わせる (うちあわせる).
Example: 私たちは新しいプロジェクトについて打ち合わせる必要があります。 (We need to discuss/arrange the new project.)
You can also say [Person A] と [Person B] が打ち合わせる。 (Person A and Person B are meeting/discussing.)

The noun form is 打ち合わせ (うちあわせ). This refers to 'a meeting' or 'a discussion.' It's very common to say, 今日の打ち合わせは午後3時からです。 (Today's meeting/discussion is from 3 PM.) or 打ち合わせがあります。 (I have a meeting/discussion.)

打ち合わせる usually falls somewhere in the middle. It's more formal than a casual chat with friends but less formal than a full-blown 会議 (かいぎ). It implies a structured discussion with a purpose, but often in a more relaxed atmosphere than a very formal meeting. Think of it as a collaborative discussion rather than a presentation.

That's a good grammar question! 打ち合わせる can be used both transitively and intransitively.
Intransitive: 私たちは明日打ち合わせます。 (We will meet/discuss tomorrow.)
Transitive: 私たちはプロジェクトの詳細を打ち合わせます。 (We will discuss/coordinate the project details.) In the transitive sense, the object is what's being discussed or arranged.

While 打ち合わせる involves discussing and arranging, it's not typically used to mean 'scheduling' in the sense of setting a date/time. For scheduling, you'd usually use words like 予定を決める (よていをきめる), meaning 'to decide on a schedule,' or アポイントを取る (アポイントをとる), meaning 'to make an appointment.' 打ち合わせる is more about the content of what's being discussed once a meeting is arranged.

A common and polite way to suggest a meeting using this word would be:
「一度、打ち合わせをしましょう。」 (Let's have a discussion/meeting sometime.)
Or, if you're talking about a specific topic:
「その件について、一度打ち合わせさせていただけませんか？」 (Regarding that matter, could we have a meeting/discussion once? - This is very polite.)

A common mistake is using it for purely social gatherings or for very formal, large-scale conferences. Remember, it's best suited for business or project-related discussions where coordination and arrangement are key. Also, sometimes learners might overuse it when simpler verbs like 話す (はなす) 'to talk' or 議論する (ぎろんする) 'to debate' would be more natural depending on the nuance.

The 'uchi' (打ち) in 打ち合わせる carries a nuance of 'striking,' 'hitting,' or 'arranging together.' Think of it as 'striking a balance' or 'bouncing ideas off each other' to reach a consensus or arrangement. The 'awaseru' (合わせる) means 'to put together' or 'to combine.' So, together, they imply a process of joint discussion and coordination to bring things into alignment.