The third fused negative, and the rule it quietly breaks
Two Serbian verbs fuse не into a single word instead of writing it separately - everyone who has met нисам and немам knows this much. A third joins them once Futur I enters the picture, and all three share something more useful than a spelling rule: fusing the negation strips the enclitic status right off the word, which is exactly why a sentence is allowed to start with one of them.
An earlier lesson on this platform already covers the basics: most Serbian verbs negate with a plain не standing separately in front of them, and exactly two common ones fuse it into a single word instead - бити becomes нисам/ниси/није…, and имати becomes немам/немаш/нема… That lesson calls these two the only verbs with a fused negative form, and for the material it covers, that is exactly right. It is scoped to the present tense taught at that level. Once Futur I enters the picture, a third fused form joins the set.
The third member: нећу
Хтети, in its role as the future auxiliary, fuses не exactly the way бити and имати do: ћу/ћеш/ће… becomes нећу/нећеш/неће… A separate не хоћу written as two words is exactly as wrong, for exactly the same reason, as writing не сам or не имам instead of нисам or немам.
Neću doći sutra.
I won't come tomorrow.
Fused from the start - there is no unfused не ћу доћи to fall back on.
What fusion actually changes: stress, not just spelling
This blog's article on second position established that сам, ћу and their families are enclitics: unstressed, unable to open a sentence, always leaning on whatever stressed word comes before them. Negating them does something more than swap in a new spelling - it removes the enclitic status entirely. Нисам, немам and нећу carry their own stress and behave like any ordinary independent verb, which is exactly why all three are free to do the one thing сам, имам and ћу can never do on their own: open a sentence.
Nisam siguran.
I'm not sure.
Sentence-initial and completely ordinary - compare with the impossible „*Сам сигуран.“, which needs a host word in front precisely because сам never stopped being an enclitic.
Nemam vremena.
I don't have time.
Same pattern: no host word required, because немам is not leaning on anything.
The overcorrection worth naming
A learner who has just internalised second position sometimes overcorrects: having drilled that an unstressed word can never open a sentence, they add an unnecessary pronoun in front of a fused negative out of pure habit, producing something like „Ја нисам сигуран.“ where a bare „Нисам сигуран.“ would sound perfectly native. That sentence is not wrong - dropping the subject pronoun is simply the more natural choice here, and no host word was ever required in the first place.
One test covers all three: if a form has не baked into it - нисам, немам, нећу, or нема - it can stand first in the sentence with nothing in front of it. If it is one of the plain, unfused enclitics instead - сам, имам, ћу - it cannot, and something stressed has to lead. Fusion and the second-position rule are opposites, not variations of the same thing.