Learn Hardcore Japanese: mainiti undou wo site, byouki wo yobousimasu. - By exercising every day, I prevent illness.

In English we must say “I exercise every day and prevent illness.”
In Japanese, if it’s obvious we’re talking about ourselves, 私(わたし) is just left out:

(私が) 毎日運動をして、病気を予防します。
→ The part in parentheses is usually omitted.

Depending on context, the subject could also be we, you, or people in general, but English almost always forces us to pick something, often “I” or “you.”

Why does 運動 take the particle を? Isn’t 運動する usually “to exercise”?

Yes, 運動する is a common verb meaning “to exercise.”
Grammatically, 運動 is a noun, and する is the verb “to do.”

So:

運動をする = “to do exercise”
This contracts very naturally to 運動する in both speech and writing.

In this sentence we have the て-form:

運動をして = “doing exercise / exercising”

Using を explicitly (運動をする) is a bit more formal or careful, but it’s also totally standard. In everyday speech, people often drop を and say:

毎日運動して、病気を予防します。

What exactly is the function of して here?

して is the て-form of する. The て-form can:

Connect two actions in sequence:
- “Do X and then do Y”
Show that one action is the means or cause of another:
- “By doing X, (I) do Y”
- “Do X and thereby Y”

In this sentence:

毎日運動をして、病気を予防します。

can be understood as:

“I exercise every day and (as a result) prevent illness.”
or “By exercising every day, I prevent illness.”

Both the simple “and” and the “by doing X” nuance are possible; context decides which is stronger. Here the cause/means nuance is very natural.

Why is there just a comma (、) after して instead of a word like から for “because”?

Japanese often uses the て-form + comma to show a soft cause-and-effect or means relationship without an explicit “because.”

Compare:

毎日運動して、病気を予防します。
→ “I exercise every day and (thus) prevent illness.” (neutral, natural)
毎日運動するから、病気を予防できます。
→ “Because I exercise every day, I can prevent illness.” (explicit “because”)

The version with て is:

more compact
slightly less formal than a clear “because” structure
often feels more natural in spoken and written Japanese for simple causal links

So the comma just marks the clause boundary; the causal nuance comes from the て-form, not from the comma itself.

What does 予防します mean exactly? Is it different from 防ぎます?

Both relate to prevention, but their nuance is a bit different.

予防する
- to prevent (especially illness or problems) in advance
- strongly associated with health, disease prevention, safety measures
- e.g. ワクチンで病気を予防する = “prevent disease with a vaccine”
防ぐ (防ぎます)
- to prevent / defend against / protect from
- broader use: disasters, attacks, crime, mistakes, etc.
- e.g. 事故を防ぐ = “prevent accidents”

In 毎日運動をして、病気を予防します。, 予防します is very natural because it’s about illness prevention in a somewhat formal or health-related tone (like something you’d see in a pamphlet or textbook).

Why is します used instead of する? What is the level of politeness here?

します is the polite -ます form of する.

する = plain form (casual, dictionary form)
します = polite form (used with strangers, in formal writing, etc.)

So:

病気を予防する。 (plain)
病気を予防します。 (polite)

The whole sentence is in polite style because of します.
In a casual conversation with friends, you might say:

毎日運動して、病気を予防する。

Does 予防します mean “I am preventing” (now) or “I prevent” (habitually)? What tense is this?

The -ます form (present polite) in Japanese generally covers:

present actions
future actions
habitual actions

The sentence as a whole, especially with 毎日 (every day), clearly indicates a habit:

毎日 → every day
予防します → present/habitual

So the natural English reading is:

“I exercise every day and (thereby) prevent illness”
(i.e., that’s what I generally do)

It is not a specific “I am right now preventing illness.” It’s more “This is my regular practice / this is generally true.”

Is the を after 病気 the same as the を after 運動?

Yes, both are the object marker を, but they attach to different verbs:

運動をして
→ “(I) do exercise”; 運動 is the object of する
病気を予防します
→ “(I) prevent illness”; 病気 is the object of 予防する

So the structure is:

[毎日] [運動をして]、[病気を予防します]
- Time: 毎日
- Action 1: 運動をして (“doing exercise”)
- Action 2: 病気を予防します (“prevent illness”)

Can I drop the を and say 毎日運動して、病気を予防します。?

Yes, that’s very common and natural.

Because 運動する is so frequently used, Japanese speakers often omit を with many する-verbs in casual or even fairly neutral speech:

運動をする → 運動する
勉強をする → 勉強する
仕事をする → 仕事する

So these are all fine:

毎日運動をして、病気を予防します。 (a bit more explicit/formal)
毎日運動して、病気を予防します。 (very natural, common)

Your textbooks may emphasize 運動をする first, but in real life speech you’ll hear both.

Could the sentence also be written as 病気を予防するために、毎日運動します。? What’s the difference in nuance?

Yes, that’s another natural way to say it, with a slightly different focus.

毎日運動をして、病気を予防します。
- Structure: [Action 1] して、[Action 2]
- Nuance: “I exercise every day and (thereby) prevent illness.”
- Emphasis: Two related actions, with a soft causal nuance.
病気を予防するために、毎日運動します。
- 〜ために explicitly means “in order to / for the purpose of”
- Nuance: “In order to prevent illness, I exercise every day.”
- Emphasis: Stronger focus on purpose; sounds slightly more explanatory or deliberate.

Both are correct; which one you choose depends on whether you want to emphasize purpose (ために) or just present two causally linked actions (〜て).

Does 病気 mean one specific illness or illness in general? There’s no plural marker.

病気 by itself can mean:

a specific illness (e.g., “this illness”)
illness in general (“sickness,” “disease”)

Japanese normally doesn’t mark plural for nouns the way English does. Context tells you which reading is natural.

In this sentence:

毎日運動をして、病気を予防します。

we’re talking about a general health habit, so 病気 here naturally means:

“illness in general” / “getting sick in general”

Not “one particular disease,” unless the broader context specifies that.

Why is 毎日 at the beginning? Could it come later in the sentence?

Yes, 毎日 (every day) can move around fairly freely, as long as it’s clear what it modifies. All of these are grammatically OK:

毎日運動をして、病気を予防します。
運動を毎日して、病気を予防します。
運動をして、毎日病気を予防します。 (less natural; sounds like “I prevent illness every day”)

The most natural and common is (1): putting 毎日 near the beginning, right before the main activity you repeat every day (運動をして).

Sentence-initial 毎日 clearly sets the time frame (“As for every day,…”) for the whole statement, which is why it’s preferred here.