Por que o ES ou S depois do CAN fica errado?

Silvia, "teach slangs" é o objeto direto do verbo "can" (respondendo a pergunta "He can what?"). Cai na forma infinitiva (sem "to" neste caso) em todas as pessoas:
I can teach slangs.
We can teach...
etc.
Semelhante em português a "Ele pode ensinar gírias."

Ola Silvia Cristina,na frase acima ´´he can teaches slags´´ o uso do ES está errado sim! já que o CAN é um MODAL VERB e sempre que modal verbs assim como auxiliares estiverem em uma frase o verbo principal(no caso teach) passa para o infinitivo...então certo seria he can teach slangs

Henry, não sabia que podíamos empregar slang no plural. Se não isso, existe diferença entre teach slangs e teach slang words/terms?

Márcio,

Na minha opinião, "slangs" é de uso bem incomum e é considerado incorreto por muitos. Veja um bom post sobre o assunto:

Slang vs slangs

I didn't object because I'm not hung up on it. Put "slangs" in Google and see what you get. For instance, http://mashable.com/2010/07/10/internet-slang-acronyms/ uses it and she's definitely mainstream English.

I prefer "teach slang" myself, but don't see much difference between "teach slangs" and teach "slang words." Slang is certainly a noun, and seems useful as either a countable or non-countable noun.

@ donay, obrigado pela resposta.

@ Henry, a URL que você indicou contém o seguinte post:

"If you don’t mind my correction: There no plural form “slangs”. The best alternative could be: Slang words, expressions, abbreviations, acronyms etc… Slang is an uncountable noun!
July 10, 2010 Reply"

de um falante nativo de inglês, presumo eu.

(Queira voltar lá e veja você mesmo!)

Fiz uma pesquisa para colocar mais lenha na fogueira:

Slang:
V. To attack with angry, uncontrolled language
Cambridge
. . .
Wordnik:

Slangs
1. third-person singular simple present indicative form of slang.

“Their respective slangs, though peculiar, are of the same genus.”

“Once in every three times, or thereabouts, he slangs me in front of the kids for not keeping order.”
Wordnik - Mais 28 frases com ' slangs' de diversas fontes - Verb/Noun
. . .
Sub-título:
COCHRAN HUMBLY OFFERS HIS AUTOBIOGRAPHY; SCHILLER SPILLS THE BEANS; TOOBIN SLANGS AWAY AT BOTH
TIME
. . .
Noun
slangs m
Plural form of slang.
Wiktionary
. . .
verb (used without object)
5.
to use slang or abusive language.
Dictionary.com
. . .
v. slanged, slang·ing, slangs
v.intr.
1. To use slang.
2. To use angry and abusive language: persuaded the parties to quit slanging and come to the bargaining table.
v.tr.
To attack with abusive language; vituperate.
TheFreeDictionary

Ok, google

Is 'slangs' acceptable?

and see what you get.

I purposely avoided "Are 'slangs' acceptable?" so as to emphasize the form of the word and not the practice of using slangs. (Ooops, there I go again...)

The point is, it's widely used as a plural noun.

Oi Pessoal!!! Muito obrigada.


Silvia