Learn Hardcore Japanese: sotira kara kotira ni kuruno ha muri nara, denwa de hanasou. - If coming here from there is impossible, let’s talk on the phone.

Japanese often avoids explicit personal pronouns. そちら literally means there/your side and politely refers to the listener or their location/organization. こちら is here/our side and refers to the speaker or their location. Using these sounds natural and polite, especially on the phone or between groups, and avoids overusing あなた.

Is そちら/こちら polite or casual? What about そっち/こっち?

そちら/こちら: neutral–polite. Safe in most situations, even with people you don’t know well.
そっち/こっち: casual. Use with friends/family. If you make the end of the sentence very casual (like 話そう), pairing it with そっち/こっち feels more consistent in tone.

Why is there a の before は in 来るのは?

の nominalizes the clause そちらからこちらに来る so it can function as a noun phrase. Think of it as turning coming from there to here into the topic X in the pattern X は無理.

Could I use こと instead of の (i.e., 来ることは無理)? What’s the nuance?

Both are grammatical:

来るのは無理: more concrete/immediate, common in speech.
来ることは無理: slightly more formal/abstract or policy-like. In everyday speech about a specific situation, の sounds more natural.

Why は in 来るのは無理 and not が?

Both work, but nuance differs:

来るのは無理: sets the action as the topic; often contrasts with other options (e.g., coming is impossible, but…).
来るのが無理: simply states the subject is impossible. With a follow-up proposal, the topic-marking は feels especially natural.

What’s the role of なら here? How is it different from たら, ば, or と?

なら means if it’s the case that/given that and works well with nouns/adjectives: 無理なら. It frames the second clause as a response to that condition.

たら (無理だったら): more event-like/hypothetical (when/if it turns out to be impossible).
ば (無理ならば): a bit more formal/literary.
と is for natural/automatic results and doesn’t fit suggestions well here.

Is there a nuance difference between 無理なら and 無理だったら?

Yes:

無理なら: neutral if-condition based on the idea/state of being impossible.
無理だったら: if it turns out/ends up being impossible (more situational, often used when the result will be known later).

Does 無理 sound too blunt? How can I soften it?

It can sound blunt in some contexts. Softer options:

難しいなら (if it’s difficult)
都合がつかないようなら (if you can’t make it/work out your schedule)
来られないなら (if you can’t come)
Polite: 無理でしたら / 難しければ

Why is it 来る and not 行く?

Use 来る when the movement is toward the speaker’s location (or the speaker’s side/team = こちら). Use 行く for movement away from the speaker. On the phone, こちら means where the speaker is, so inviting the listener to come to the speaker uses 来る.

Do I need both そちらから and こちらに? Can I shorten it?

You can shorten it. こちらに来るのは無理なら is perfectly natural; the starting point (そちらから) is often understood. Including そちらから simply makes from your side explicit.

Why に after こちら? Could I use へ?

Both こちらに and こちらへ are fine with motion verbs. に is the default destination marker; へ has a slightly more directional feel and is common in polite invitations (e.g., こちらへどうぞ). Meaning-wise here, there’s no big difference.

What does で do in 電話で話そう? Why not 電話に?

で marks the means/instrument: talk by phone. 電話で話す = talk using the phone. 電話に is not used for this meaning. You could also say 電話しよう/電話しましょう (let’s call), which is slightly different: call rather than explicitly talk by phone.

What’s the nuance of 話そう?

It’s the plain volitional form: a direct, casual let’s talk. Variants:

Polite: 話しましょう
Softer suggestion: 話そうか / 話しましょうか
More polite with honorific nouns/verbs: お電話でお話ししましょう

How would I make the whole sentence polite?

Examples:

そちらからこちらに来るのが無理でしたら、お電話でお話ししましょう。
Softer: こちらにいらっしゃれないようでしたら、お電話でお話ししましょう。
Even softer: こちらにお越しになるのが難しければ、お電話でお話しできればと思います。

Can I replace 来るのは無理 with potential form like 来られない?

Yes:

そちらからこちらに来られないなら、電話で話そう。 Very natural. In casual speech, many say 来れない; prescriptively 来られない is standard.

Is it okay to drop parts like こちら or そちら if context is clear?

Yes. Common short versions:

来るのが無理なら、電話で話そう。
来られないなら、電話で話そう。 Context usually supplies who goes where.

Is there any register mismatch between そちら (sounds polite) and 話そう (casual)?

It’s acceptable; そちら isn’t overly formal, and people mix levels in real speech. For fully casual, switch to そっち…話そう. For fully polite, use そちら…話しましょう and optionally add お電話/お話し.