Learn Hardcore Icelandic: Ég fer ekki út, nema veðrið sé gott. - I don't go out unless the weather is good.

Because nema here means “unless,” which introduces a hypothetical or non-factual condition. In Icelandic, that calls for the subjunctive mood (viðtengingarháttur), so you use sé (subjunctive) instead of er (indicative). If nema means “except (that)” and states a known fact, the indicative is possible. Compare:

Hypothetical “unless”: Ég fer ekki út, nema veðrið sé gott. (correct)
Factual “except that”: Allir komu, nema Jón var veikur. (“except that Jón was sick”)

What form is sé, and how do I conjugate it?

Sé is the present subjunctive of vera (to be), 3rd person singular. Present subjunctive of vera:

ég sé, þú sért, hann/hún/það sé, við séum, þið séuð, þeir/þær/þau séu For comparison, present indicative:
ég er, þú ert, hann/hún/það er, við erum, þið eruð, þeir/þær/þau eru

Can I say “Ég fer ekki út, nema veðrið er gott”?

Not when you mean “unless.” Careful speakers use the subjunctive sé after nema in this conditional sense. Using er will sound off. Stick to nema veðrið sé gott for “unless the weather is good.”

What exactly does nema mean, and are there alternatives?

Nema most often means “unless” or “except (that).” To rephrase with “if,” you can say:

Ég fer bara út, ef veðrið er gott. (“I only go out if the weather is good.”) Avoid the ambiguous “ef … ekki” for “unless”; “nema” or “bara ef” is clearer.

Do I need the comma before nema?

It’s common and perfectly fine to put a comma before a nema-clause. Many writers include it to mark the clause break; others may omit it in short sentences. You won’t be wrong with the comma here.

Should I ever write nema að?

You’ll hear and see nema að, but it’s often considered redundant in careful writing. Plain nema is standard and preferred in this sentence: Ég fer ekki út, nema veðrið sé gott.

Why is ekki placed after fer?

Main clauses in Icelandic are verb-second (V2), so the finite verb typically comes second. The negation ekki follows the verb: Ég fer ekki út. In the nema clause, if you wanted to negate “good,” you’d place ekki before the adjective: nema veðrið sé ekki gott.

Why is it út and not úti?

út indicates motion outward (“out”), so it pairs with verbs of movement: fara út “go out.”
úti indicates location (“outside”): vera úti “be outside.” Your sentence has movement, so út is correct.

What’s going on with veðrið? Why the definite form?

Veðrið is the definite nominative singular of the neuter noun veður (“weather”). Icelandic commonly uses the definite article when talking about “the weather” in a specific time frame: veðrið. The indefinite veður is possible in other contexts, but here veðrið is the natural choice.

Why is the adjective gott and not góður?

Adjectives agree with the noun they describe in gender, number, and case. Veðrið is neuter singular nominative, so the adjective takes the neuter form: gott (from góður/góð/gott). Hence: veðrið er/sé gott.

What are the present forms of fara, and why is it fer?

Fara is irregular. Present indicative:

ég fer, þú ferð, hann/hún/það fer
við förum, þið farið, þeir/þær/þau fara So ég fer is the correct 1st person singular form.

Why is the present tense (fer) used when English might say “I won’t go out …”?

Icelandic often uses the present tense for general rules, habits, and near-future plans. Ég fer ekki út, nema … naturally expresses a standing condition. You can use the future auxiliary munu if you want: Ég mun ekki fara út, nema veðrið sé gott. Note that sé still fits well; verði (“become”) would suggest a change and isn’t necessary here.

Does the verb still go second in the nema clause?

No. In subordinate clauses, the verb doesn’t move to second position as in main clauses. The order is typically Subject–Verb–(Negation)–Rest:

nema veðrið sé (ekki) gott. In the main clause: Ég fer (V2) ekki út.

How would I say “I am outside unless the weather is bad” to practice úti vs út?

Movement: Ég fer út, nema veðrið sé gott. (“I go out unless the weather is good.”)
Location: Ég er úti, nema veðrið sé vont. (“I am outside unless the weather is bad.”)

Any lookalike forms I should avoid mixing up with sé?

Yes: sé (subjunctive of “to be”) vs séð (“seen,” the past participle of sjá, “to see”). They’re different words and functions:

nema veðrið sé gott (subjunctive “be”)
Ég hef séð hann (I have seen him)

Can I front something for emphasis and still keep it correct?

Yes. Icelandic keeps V2 in the main clause even when you front another element:

Út fer ég ekki, nema veðrið sé gott. This is more emphatic/stylistic but grammatical.