Learn Hardcore Japanese: tomodati to issyo ni hanasu to, sabisisa ga sukosi herimasu. - When I talk together with a friend, my loneliness decreases a little.

In this sentence, 友達と一緒に話す literally means “talk together with (my) friend(s).” The と is the standard particle for “with (someone)” in the sense of doing something together or interacting with them (talk, fight, play, etc.).

If と already means “with,” why do we also need 一緒に? What’s the difference between 友達と話す and 友達と一緒に話す?

You don’t strictly need 一緒に; it adds nuance.

友達と話す
→ “I talk with my friend(s).” (basic, neutral)
友達と一緒に話す
→ “I talk together with my friend(s).” (slightly more explicit about togetherness / companionship)

一緒に literally means “together,” so 友達と一緒に emphasizes the feeling of doing something side by side. In this sentence, that matches the emotional idea that talking together with friends helps reduce loneliness.

You could say 友達と話すと、寂しさが少し減ります。 and it would still be natural, just a little less “together”-sounding.

Why is 一緒 followed by the particle に (一緒に)? What does 一緒に do grammatically?

一緒 is a noun meaning “together,” and it often becomes an adverb with に:

一緒 (together, as a concept)
一緒に (together, as an adverb modifying the verb)

So 一緒に話す literally means “to talk in a ‘together’ way” → “to talk together.”

Grammatically:

一緒に is an adverb.
It modifies the verb 話す (“talk”), telling us how the talking happens.

This Noun + に pattern is common for making adverb-like expressions, e.g.:

静かに話す – to speak quietly
早く歩く – to walk quickly
(早く is the adverb form of 早い, but the idea is similar: an adverb modifying the verb.)

Why is the verb 話す in dictionary/plain form before と? What does ～と mean here?

Here, 話すと is using と as a conditional marker meaning “when / if (you) talk.”

Pattern:

[plain form verb] + と, e.g.
話すと = “when/if (I) talk”
食べると = “when/if (I) eat”

This type of と-conditional often means:

“Whenever A happens, B (naturally) happens.”
“When A happens, then B follows (as a result).”

So:

友達と一緒に話すと、寂しさが少し減ります。
→ “When (I) talk with my friends, (my) loneliness decreases a little.”

The verb before と must be in plain form (dictionary form or past plain form), not in ます-form.

Why is it 寂しさ instead of 寂しい? What does the ending ～さ mean?

寂しい (さびしい) is the adjective “lonely.”

Japanese often turns adjectives into abstract nouns by adding ～さ:

寂しい → 寂しさ = “loneliness”
高い → 高さ = “height”
うれしい → うれしさ = “(feeling of) happiness”

So:

寂しさ literally means “the feeling/state of being lonely,” i.e. loneliness.

In this sentence, sadness / loneliness is being treated as a thing that can increase or decrease, so the noun form 寂しさ is used rather than the adjective 寂しい.

Why is the particle が used with 寂しさ instead of は or を?

Here, 寂しさ is the subject of the verb 減ります (“decreases”). The particle が marks the subject of many intransitive verbs.

寂しさが減ります。
→ “Loneliness decreases.” (Loneliness = the thing that changes on its own.)

Some contrasts:

寂しさが減る
→ neutral statement about what is decreasing (subject).
寂しさは減る
→ makes 寂しさ the topic (“As for loneliness, it decreases…”), slightly shifting focus or implying contrast with something else.
Using を would be ungrammatical here, because 減ります in this form is intransitive; it doesn’t take a direct object.

So が is natural: it marks “loneliness” as the thing that is changing.

What’s the nuance of 減ります here? Why not 減らします?

Japanese often has transitive / intransitive verb pairs:

減る (intransitive) – “to decrease (by itself)”
→ 寂しさが減る = “loneliness decreases”
減らす (transitive) – “to decrease/reduce (something)”
→ 寂しさを減らす = “to reduce loneliness”

In the sentence, the intransitive 減ります is used:

寂しさが少し減ります。
→ “(My) loneliness decreases a little.”

This focuses on the state of loneliness changing, rather than on you actively reducing it. In English, both can sound like “it reduces,” but in Japanese the choice affects who/what is grammatically doing the action.

減らします would be like:

友達と一緒に話すと、寂しさを少し減らします。
→ “When I talk with friends, I reduce my loneliness a little.”
This is grammatically fine, but sounds a bit more “I actively reduce it,” whereas the original is softer and more about the natural effect.

What does 少し modify? Is it “a little loneliness” or “decreases a little”?

In this sentence, 少し modifies the verb 減ります, not 寂しさ:

寂しさが少し減ります。
→ “Loneliness decreases a little.”

If it were “a little loneliness” in the sense of “a small amount of loneliness exists,” you’d usually see a different structure, e.g.:

寂しさが少しあります。 – “There is a little loneliness.”

Here, the idea is:

The amount of loneliness goes down by a small amount.
So: “It gets a bit less lonely.”

What politeness level is 減ります? Could I say 減る instead?

減ります is the polite ます-form of 減る.

Plain: 減る
Polite: 減ります

Using 減ります makes the whole sentence politely neutral, suitable for talking to people you’re not very close to, in class, etc.

You can say:

友達と一緒に話すと、寂しさが少し減る。

That’s the plain form and is natural in casual conversation with friends or family, or in inner monologue. Just be consistent: once you switch to plain style, other verbs in the same context usually also stay plain.

Is the word order fixed? Could I move 少し or 一緒に around?

Japanese word order is flexible, but some positions sound more natural than others.

The original:

友達と一緒に話すと、寂しさが少し減ります。

Natural variations:

友達と一緒に話すと、寂しさが少し減ります。 (original)
友達と話すと、寂しさが少し減ります。 (dropping 一緒に)
友達と一緒に話すと、少し寂しさが減ります。 (ok; slightly different rhythm)

Unnatural or awkward:

✕ 寂しさが減ります少し。
✕ 友達と少し一緒に話すと、寂しさが減ります。 (this suggests you only talk together a little, not that the loneliness decreases a little)

General idea:

Adverbs like 少し usually come just before the verb they modify or before が-marked nouns if the nuance fits.
一緒に usually appears right before the verb it modifies (話す).