"Um número de": plural or singular?
In the discussion of the sentence "A number of different letters appear on the screen" the featured answer is "Várias letras diferentes aparecem na tela". The more obvious translation is to swap "Várias" for "Um número de" to get "Um número de letras diferentes aparecem na tela".
I would have been happy with that answer if I hadn't found this quote:
The number of devices in this pack is twenty (O número de componentes neste pacote é vinte)
A number of devices are not included in this pack (um número de componentes não foi incluído neste pacote).
Observe que, diferentemente do português, em que a segunda forma se mantém no singular, no inglês, ela vai para o plural.
This implies that although "a number of" is plural, "um número de" is singular. Therefore the correct translation should not use "aparecem" but "aparece" instead, to give: "Um número de letras diferentes aparece na tela".
Sometimes plural/singular questions are difficult to decide and you go with your instincts as a native speaker. Every so often you find that usage has been set in stone by grammarians and your instinct fails. Is this one of those cases? It is difficult to decide based on example sentences because even good writers make mistakes.
Although I would welcome any comments, a link to something definitive would be worth a Lingot or two. :-)
As a native portuguese speacher who completed high school, I can say to you that, in this particular case, "número" may work like a collective noun. Knowing this and one verbal concordance rule which says that you can focus either on the collective noun or on what the collective noun reffers to (de componentes), you solve the problem. So, it can be both "um número de componentes não foi incluído neste pacote" or "um número de componentes não foram incluídos neste pacote". You can read it here (http://www.infoescola.com/portugues/concordancia-verbal/) on the item "SUJEITO COLETIVO (SUJEITO SIMPLES)".
Thanks. Thanks too for your answer in the original discussion: http://www.duolingo.com/comment/929153 (another Lingot there :-)
What you say is true of a number of collective nouns in English (although British and American English usage can differ: http://en.wikipedia.org/wiki/Collective_noun).
This discussion talks about "a number of" in English: http://www.dailywritingtips.com/is-number-singular-or-plural/. The author basically says it is always plural, and one of the comments sums it up by saying "Because the object of the preposition for 'a number of' will always be plural, we need the plural form of the verb". This is obviously not true for "um número de" because we have seen an example where it takes the singular form of the verb so that still leaves room for doubt.
Yes, you entered on the misty field of grammar discussion. Number in portuguese works just as this link http://www.dailywritingtips.com/is-number-singular-or-plural/ said it works in english. For the sintax analysis he provided, I am not sure. My suposition is all based that "um número de" may be analyzed as a collective, but this depends on the context (in that case, that the number is higher than one). What I done there is called "silepse" event on verbal concordance (you focus on the idea, not on a common view on what is written).
I sometimes ignore the grammar of my own language when it seems absurd to me. With Portuguese I still need to learn the rules before I can break them. In this case I would have no difficulty at all if I had not read the article which mentioned "um número de componentes". Maybe the guy is simply wrong!
I edited the above post in regard to that link of number being either singular or plural. I do not know the principle in english grammar in the sentence, for instance, "a significant number of bricklayers lay bricks", but to me it seems to "a significant number" have a similar function of a collective and that "number" can not perform an action, therefore the verb may not be singular. In portuguese, it would be "um número significativo de pedreiros coloca(m) tijolos", and that event of collective or "silepse" concordance would occur (you normally think that "significativo" means more than one).
The only problem I see is the mecanism of the concordance. Portuguese and English have some similarities, but not too many in special cases of concordance, so we need to be aware. Try to use the rules you know, and, when you learn new rules, defy the ones you knew before with special situations.
Thanks for your help. It is tempting to impose the English rule (never singular) on the Portuguese sentence because that would make life easier, but as with preposition choice, Portuguese is not designed to make life easy for a learner who speaks English. :-)
Oh, I forgot to mention this site which talks about collective nouns: http://www.economist.com/style-guide/singular-or-plural. It covers this case, but more interestingly it includes the example "law and order" which looks plural but is actually singular (which just goes to show that sometimes you can't trust your instincts).
I agree Gcalbe, I know you are right because is the same in spanish, my mother language. Thank you