Friends tell me there is a subtle difference between the two, and that jamás is a little stronger, a little more definitive a statement than nunca.
Both mean "never"—but are there any measurable differences? Places where you'd use one and not the other?
It is easy to find nunca and jamás occurring in free variation within the same paragraph, even within the same sentence, with absolutely no difference in meaning intended. So while in many instances there is little to no difference between them, sometimes there can be. In their entry on the historical origin of jamás, this Chilean website on Etymologies succinctly summarizes the principal difference this way:
Jamás substitue, enfáticamente, a nunca.
That is, jamás is an emphatic version of nunca — now. The actual history of the word jamás is interesting, deriving from a Latin expression literally meaning ya más. However, over the years it eventually changed its meaning to the very opposite of that — to meaning nunca — which is the prevailing situation in our day.
However, if you read medieval Spanish, be prepared to find jamás sometimes used in the sense of siempre instead of as nunca. See Llorens 1929, “La negación en español antiguo con referencias a otros idiomas” in Revista de Filología Española for more on this.
If the scholarly Chilean site is correct about jamás being more emphatic than nunca, then it would make sense for jamás to occur with less frequency than nunca, since emphasis is less common than not emphasizing something.
And in fact, this is precisely what we find in Google Books: nunca is certainly the more common of the two, occurring about four times as often as jamás does in Google Books’ Spanish corpus:
If you click on the graph, it should take you to the original.
There could of course be other reasons for the frequency disparity than that of emphasis. It is evidence, not proof.
Another difference between the two can be found in certain fixed collocations where you must use one but not the other, or vice versa.
For example, nunca jamás and siempre jamás are fixed forms with specific meanings, and if you swap nunca for jamás in them, you break them. The opposite versions are virtually never seen per this Google N-gram:
If you click on the graph, it should take you to the original.
There are a few scant instances of jamás nunca to be found, but nunca jamás is the normal formulation. Siempre nunca virtually never occurs, as you cannot turn nunca into a positive instead of a negative the way you can in siempre jamás.
In the paper “Negación doble y negación simple en español moderno” published in issue 9 of Revista de Filología Románica in 1992, Bergareche on page 65 lists the negative adverbs nunca, jamás, and tampoco, where he observes that:
Nunca, que procede de una palabra negativa latina, NUNQUAM, constituye la negación de tiempo en español, el correlato negativo de siempre.
Jamás, de etimología positiva, IAM MAGIS, funciona de modo idéntico a nunca con la salvedad de que puede servir de refuerzo a ese mismo adverbio, e incluso también a siempre, en este caso con sentido positivo. Existe un uso sustantivo de jamás, que no nos interesa aquí por razones ya expuestas anteriormente, en la expresión «jamás de los jamases».
In his examples, he makes no distinction between these two with regard to negatives.
Consider possible negative answers to questions like these:
One could negatively answer those questions with such answers as: (this is not exhaustive)
Some but not all speakers distinguish case 3 from case 4 in that the former means you hadn’t but weren’t ruling out doing so in the future, whereas the latter says you have no intention of ever doing so either. If that distinction matters, seek clarification, because not everyone will agree on the difference.
Case 5 is stronger, reinforcing the “neverness”. However, while it might mean “absolutely never”, it might also in the right context also mean “never again” or “never more”. For example, if you’d tasted the pulpo but it didn’t agree with you, you might say:
I have usually seen these two words used together, for emphasis. This is perhaps better understood as being similar to the way we say "never ever" in English.
"jamas" is a subtle slang synonym of "nunca". I would say "jamas" is more emphatic as "absolutely never". Look up the English translation for both words to see their definitions and in what contexts they're used.
