What part of speech is "нельзя"? I see so many Russian dictionaries say it is used as a predicative complement (предикатив), but none of the ones I saw would "dare" state it as an adverb (наречие).
Debates around the group of words
нельзя, можно, надо, жаль, пора, грех, стыд, неохота, больно ( в безличных предложениях)etc.
have been going since 1928, when Щерба Л.В. wrote his article «О частях речи в русском языке».("Word classes in Russian ). He said it's difficult to refer these words to any of the existing "parts of speech ". He called them "a category of state"(категория состояния). Some linguists call them "predicatives"
Предикативы--особая группа слов, стоящая вне традиционной системы частей речи и обозначающих нединамическое состояние.
This term has no official status. This terminology is often criticized because it can be confused with sentence constituents (subject, predicate, etc) Other linguists refer these words to a special category of adverbs or even "modal adverbs". For more information see
Predicative is an ambiguous term that can also mean a part of sentence and include adjectives, adverbs and participles. So I do not recommend using this term.
There are linguists who propose a separate part of speech, called категория состояния, that is, category of state. They count нельзя as such part of speech. Examples:
У меня на душе спокойно (category of state);
Река течёт спокойно (adverb);
Дитя спокойно (adjective).
In short, it is something like an adverb or adjective but without a verb or noun to which it relates. Something like dark in "It is dark now". In English "it" and "is" are mandatory, so dark is adjective related to it. In Russian they can be omitted: "dark now here".
Some categories of state have forms similar to adjectives and adverbs (like спокойно) but others do not, and can be used only as category of state: можно, надо, нельзя, жаль.
Some coincide with nouns in form: грех, стыд, охота, неохота.
Inside category of state it is separated the class of modal categories of state. These words include нужно, можно, надо, нельзя, жаль, незачем.
So, most precise, нельзя is modal category of state. The old term for it in 1980s was "predicative", as a class of adverbs.
Maybe a usual contemporary dictionary says that 'Нельзя' is a predicative. But not all linguists are agree to separate predicatives to a specific part of speech. In our old schoolbooks this word was assigned to adverbs. I am not a professional linguist and I think predicatives are rather a matter of syntax, than of grammar. So, I'm comfortable "to state it as an adverb" )
нельзя is a predicative adverb, as a word class in morphology (предикативное наречие).
It is used as a predicate, as part of the sentence, in syntaxis (сказуемое).
(predicative also belongs to syntaxis, when the predicate is composed with an helping verb).
We may think that the word есть is missing: нельзя = является не лёгким, можно = есть возможным.
This is a logical classification, and it leans towards the 'latin' grammar which is appropriate to indogerman languages. And russian is a quite near to latin (latvian, lithuan even more antique than russian). My exact source is Шелякин, справочник по русской грамматике, М.: Рус.яз., 2003. The Oxford Russian Dictionary, too, gives нельзя as adverbe.