Learn Hardcore Japanese: watasi ha ookina kouen de inu to issyo ni sanposimasu.

私は = As for me / Talking about me…
It sets 私 as the thing we’re talking about, and then the rest of the sentence explains something about that topic.

が is the subject marker, used when:

introducing something new,
emphasizing who did the action,
or in certain fixed patterns.

In a simple, neutral sentence like this—“I walk with my dog in a big park”—Japanese usually uses は to present “I” as the topic of the sentence.
Using 私が大きな公園で…散歩します would feel like you’re emphasizing “I (and not someone else) am the one who walks,” which is not needed here.

Is 私 necessary here, or can it be omitted in natural Japanese?

私 can absolutely be omitted, and often is in natural Japanese.

You could say:

（私は）大きな公園で犬と一緒に散歩します。

Because the subject (“I”) is usually clear from context, Japanese speakers often leave 私 out unless:

it’s needed to avoid ambiguity, or
they specifically want to emphasize “I”.

So in everyday conversation, 大きな公園で犬と一緒に散歩します would sound perfectly natural as “I take walks with my dog in a big park.”

What’s the difference between 大きな公園 and 大きい公園? Are both correct?

Both are correct, but there is a small nuance.

大きい公園
- Uses the regular い-adjective form 大きい before a noun.
- Very common and neutral in spoken Japanese.
大きな公園
- Uses the attributive form 大きな (used only before nouns).
- Feels a bit more literary or slightly formal / descriptive.
- Often used in writing, stories, or when you want a slightly more “narrative” or “poetic” tone.

Meaning-wise, both are “big park.”
You can almost always switch between them without changing the core meaning:

大きい公園で散歩します。
大きな公園で散歩します。

What does the particle で do after 公園, and how is it different from using に or へ?

で marks the place where an action happens.

公園で散歩します。
= “I take a walk in the park” (the park is the location of the action).

Compare:

公園に行きます。
= “I go to the park.” (に/へ mark the destination of movement.)
公園で行きます。
(unnatural) — で is not used for a destination; it’s for the place where you do something.

So in this sentence, 公園で is correct because the walking itself happens in the park. If you said 公園に散歩します, it would sound wrong in standard Japanese.

Why is と used after 犬, and does it always mean “with”?

In 犬と一緒に, the particle と means “with” (together with).

Common uses of と:

“A and B” (listing)
- 犬と猫 = “dogs and cats”
“With” (together with someone)
- 友達と行きます。 = “I go with my friend.”
Quoting / thought / speech marker (e.g. …と言いました)

Here, 犬と一緒に literally means “together with the dog.”
So と is marking the companion in the action: 散歩します “(I) take a walk” with the dog.

Why do we have both 犬と and 一緒に? Isn’t using both “with” words redundant?

It looks redundant from an English perspective, but in Japanese this is a very natural, common pattern.

犬と散歩します。
= “I take a walk with my dog.” (Perfectly fine.)
犬と一緒に散歩します。
= Literally “I, together with my dog, take a walk.”
This makes the “togetherness” a bit more explicit or emphasized.

You can think of 犬と一緒に as a fixed chunk meaning “together with my dog.”

So:

犬と散歩します → simple “with my dog”
犬と一緒に散歩します → “together with my dog,” slightly more vivid or explicit

Both are correct; the version with 一緒に just leans into the “together” feeling.

What exactly is 一緒に grammatically, and why does it use に instead of another particle?

一緒 (いっしょ) is originally a noun meaning “together / the same.”
When you add に, it becomes an adverb, “together.”

一緒に = “together” (used to modify a verb)

に here is not a location marker; it’s a common way of turning certain nouns into adverbs. Some parallels:

安全に = safely
簡単に = easily
一緒に = together

In the phrase 犬と一緒に散歩します:

犬と = “with my dog”
一緒に = “together” (adverb modifying 散歩します)

So we don’t need another particle after 一緒; the whole set 犬と一緒に acts as “together with my dog.”

What’s the difference between 散歩します and 歩きます? Both seem to mean “walk.”

They are related but not the same:

歩きます (あるきます)
= “to walk” (the physical action of walking, moving your feet)
- 駅まで歩きます。 = “I walk to the station.”
散歩します (さんぽします)
= “to take a walk / go for a stroll” (as an activity, often for relaxation or exercise)
- 公園で散歩します。 = “I take a walk in the park.”

So:

If you want to stress “I’m walking to somewhere,” use 歩きます.
If you mean “I’m going on a walk (as an activity),” especially with a dog, 散歩します is the natural verb.

With a dog, 犬と散歩します is the standard phrase for “I walk my dog / go for a walk with my dog.”

Why is there no を (object marker) in this sentence? Isn’t there an object of 散歩します?

In 散歩します, the noun 散歩 (“a walk”) is turned into a verb phrase “to take a walk.”
This is a common pattern: [Noun] + します → “to do [noun].”

勉強します = “to study” (literally “do study”)
運動します = “to exercise”
散歩します = “to take a walk”

Because 散歩します is used as a verb by itself, it doesn’t require a direct object with を here. The sentence is just:

(Topic) 私は
(Location) 大きな公園で = in a big park
(Companion) 犬と一緒に = together with my dog
(Verb) 散歩します = take a walk

There’s no separate “thing” being acted on that needs を.

How would I change this sentence to past tense or casual form?

Base sentence (polite present/future):

私は大きな公園で犬と一緒に散歩します。
= I take walks / will take a walk…

1. Polite past tense
Change します → しました:

私は大きな公園で犬と一緒に散歩しました。
= I took a walk with my dog in a big park.

2. Casual present/future
Change 散歩します → 散歩する and usually drop 私:

大きな公園で犬と一緒に散歩する。
= (I) take walks / will take a walk…

3. Casual past
Change 散歩する → 散歩した:

大きな公園で犬と一緒に散歩した。
= (I) took a walk with my dog in a big park.

Politeness is mainly carried by the ます / ました part.

Does 犬 here mean “a dog” or “my dog”? How do you specify “my dog” in Japanese?

On its own, 犬 is just “dog”—neither clearly “a dog” nor “my dog.”
Japanese often leaves possession to context.

In a sentence like 犬と一緒に散歩します, if you’re talking about your daily routine, listeners will naturally understand it as “my/our dog.”

If you need to be explicit:

私の犬と一緒に散歩します。 = I walk with my dog.
飼っている犬と一緒に散歩します。 = I walk with the dog I keep / my pet dog.

But in normal conversation, just 犬と一緒に散歩します is usually enough to imply “with my dog.”

Can the word order be changed, or must it stay as 私は大きな公園で犬と一緒に散歩します?

Japanese word order is fairly flexible as long as the verb comes at the end.
You can rearrange the other parts without changing the basic meaning.

Some natural variations:

私は犬と一緒に大きな公園で散歩します。
大きな公園で私は犬と一緒に散歩します。
犬と一緒に私は大きな公園で散歩します。 (a bit marked/emphasized)

The most neutral, natural orders are usually:

私は大きな公園で犬と一緒に散歩します。
私は犬と一緒に大きな公園で散歩します。

Just make sure:

the main verb (散歩します) stays at the end, and
particles (は, で, と, に) stay attached to the correct words.

Is 散歩します always polite? How do I say the same thing very casually to a friend?

Yes, 散歩します is in the polite form (ます-form).

Casual (plain) forms:

Present/future casual: 散歩する
- 大きな公園で犬と一緒に散歩する。
Past casual: 散歩した
- 大きな公園で犬と一緒に散歩した。

In casual conversation with friends, you’d typically:

drop 私, and
use 散歩する / 散歩した instead of 散歩します / 散歩しました.