Learn Hardcore Filipino: Huwag siyang umalis mag-isa kung gabi.

In prohibitions and commands, Tagalog often uses the imperative/neutral form, which for many -um- verbs looks identical to the completed form. So Huwag (kang/siyang) umalis means “Don’t leave,” not “Don’t left.” The aspect here is overridden by the imperative/prohibitive mood triggered by huwag.

What exactly is siyang in Huwag siyang umalis?

It’s siya + -ng (the linker). When a pronoun like siya appears before a verb phrase in this kind of construction, the linker -ng attaches to it: Huwag siyang umalis. Think of the pattern: Huwag + [subject pronoun + -ng] + verb.

Can I say Huwag siya umalis or Huwag umalis siya instead?

Huwag siya umalis is ungrammatical.
Huwag umalis siya is generally avoided with pronouns; use Huwag siyang umalis.
With names or nouns you can place the subject after the verb: Huwag umalis si Maria / ang guro. But with siya, stick to Huwag siyang umalis.

How is Huwag siyang umalis different from Huwag kang umalis?

Huwag siyang umalis talks about a third person (he/she shouldn’t leave).
Huwag kang umalis is addressed directly to the listener (you shouldn’t leave). Here kang = ka + -ng.

Should there be nang before mag-isa? I often see umalis nang mag-isa.

Using nang before a manner phrase is standard and clearer: Huwag siyang umalis nang mag-isa. In casual speech, people sometimes omit nang and say umalis mag-isa, but nang is recommended, especially in writing.

What’s the difference between kung gabi, kapag gabi, sa gabi, and tuwing gabi?

kung gabi / kapag gabi: “when it’s night/at night” (conditional/temporal; kapag is a bit more formal).
sa gabi: “at night” (locative time marker; neutral).
tuwing gabi: “every night” (habitual). All fit this sentence, with slight nuance differences.

Is kung always “if”? Why is it used for time here?

Kung can mean “if” or “when,” and it’s commonly used with general time expressions: kung gabi = “when it’s nighttime/at night.” Kapag is a near-synonym that some consider stylistically more formal for “when.”

Can I move the time phrase to the front: Kung gabi, huwag siyang umalis mag-isa?

Yes. Time expressions can be fronted for emphasis: Kung gabi, huwag siyang umalis (nang) mag-isa.

Why is mag-isa hyphenated?

It’s mag- + isa (“alone”) and is conventionally hyphenated: mag-isa. You’ll also see it as a predicate: Mag-isa siya (“He/She is alone”).

Is mag-isa an adjective, adverb, or a verb?

It functions as:

A predicate/statative verb: Mag-isa siya (“He/She is alone”).
A manner adverb with a verb: umalis (nang) mag-isa (“leave alone”). Both are natural in Tagalog.

What’s the nuance difference between umalis and lumabas here?

umalis = leave/depart (from a place/situation).
lumabas = go outside/go out (to the outside). For safety contexts, both occur: Huwag siyang lumabas (nang) mag-isa sa gabi emphasizes not going outside; umalis emphasizes not departing alone.

Do I need an article like ang/si with siya?

No. Siya already serves as the nominative subject pronoun. With nouns/proper names you’d use ang/si (e.g., Huwag umalis si Juan), but with siya, use Huwag siyang umalis.

Could I say Huwag mo siyang payagang umalis (nang) mag-isa kung gabi if I want to tell someone not to allow it?

Yes. That explicitly commands the listener not to permit the third person to leave alone at night. It’s clearer than Huwag siyang umalis when you’re instructing a guardian/other person.

Is wag acceptable instead of huwag?

Wag is common in texting/casual speech. Huwag is the standard spelling and preferred in formal writing.

Why does umalis start with um-? Where did that come from?

The -um- infix marks actor-focus intransitive verbs. With vowel-initial roots like alis, -um- surfaces as a prefix-like um- → umalis.

Do I ever use aalis here?

Not in a prohibition. Use umalis after huwag for “don’t leave.” Aalis is the contemplated/future aspect (“will leave”) used in statements like Aalis siya mamaya (“He/She will leave later”).

Can I intensify the time part to mean “late at night”?

Yes:

gabing-gabi = very late at night: Huwag siyang umalis (nang) mag-isa gabing-gabi.
hatinggabi = midnight: Huwag siyang umalis (nang) mag-isa sa hatinggabi.