Double negation. A common mistake that the spaniards usually do.
"No he estudiado nada"
"No quiero nada"
"Yo no lo sé tampoco"
"No veo nada"
"No tiene ninguna gracia"

(etc.)

In our language (spanish) it's very common to use the double negation to express something in negative like the examples above. Nevertheless, if you think about it, you'll realise that these sentences have no sense at all, because you are negating the negation, but we have accustomed to understand these sorts of sentences in our own way.

However, I would like you to help me with the matter, because the expressions above are expressions that I usually use in my way of thinking. I'll try to learn your advice so that I can use it like a reflex when I try to express something similar. Thanks a lot!

Question

Double negation. A common mistake that the spaniards usually do.
"No he estudiado nada"
"No quiero nada"
"Yo no lo sé tampoco"
"No veo nada"
"No tiene ninguna gracia"

(etc.)

In our language (spanish) it's very common to use the double negation to express something in negative like the examples above. Nevertheless, if you think about it, you'll realise that these sentences have no sense at all, because you are negating the negation, but we have accustomed to understand these sorts of sentences in our own way.

However, I would like you to help me with the matter, because the expressions above are expressions that I usually use in my way of thinking. I'll try to learn your advice so that I can use it like a reflex when I try to express something similar. Thanks a lot!

Answer

I'm not a teacher.

In English, a double negative IS considered incorrect. In a native English speaker it gives the impression of being careless, sloppy, or uneducated. If you are trying to learn correct English you should try to avoid it.

But don't worry: it will not be misunderstood. Despite the apparent "logic," it is a myth that "a double negative makes a positive."

In colloquial speech, a double negative will always be understood as an intensification of the negative.

"I ain’t got no time for supper" will be understood as "I don't have time for supper."

"I can't find no place to park" will be understood as "I can't find a place to park."

"I don't have nobody to mow the lawn" will be understood as "I don't have anybody to mow the lawn."

The only exception to this I can think of is a literary affectation used by educated people: the "not un-" construction. It expresses a weak or vague positive. "a not unjustifiable assumption" means "possibly a justifiable assumption."

Answer

Dan Smith's post is excellent.

Another possible, and non-colloquial, use of the double negative is the "not not" construction.  Examples:   "Will you please tell a lie for me?" -- "No, I can not* not tell the truth." =  "I must tell the truth."  ///   "Don't help him."  --  "He's my best friend.  I will not not help him." =  "I will help him."

*can not is more often written as cannot

Answer

I'm not a teacher. In English, a double negative IS considered incorrect. In a native English speaker it gives the impression of being careless, sloppy, or uneducated. If you are trying to learn correct English you should try to avoid it.

BUT don't worry: it will NEVER be misunderstood. Despite the apparent "logic," it is a myth that "a double negative makes a positive." In colloquial speech, a double negative will always be UNDERSTOOD as an intensification of the negative.

"I ain’t got no time for supper" will be UNDERSTOOD as "I don't have time for supper."
"I can't find no place to park" will be UNDERSTOOD as "I can't find a place to park."
"I don't have nobody to mow the lawn" will be UNDERSTOOD as "I don't have anybody to mow the lawn."

The only exception to this I can think of is a literary affectation used by educated people: the "not un-" construction.
"a not unjustifiable assumption" means "possibly a justifiable assumption."