If your.definition of learning is similar to that of Krashen, the answer is almost certainly both. 

In my opinion, as adults we consciously learn -- not acquire --  an additional language.

"Second language acquisition" is a widely used expression. It is a  convenient phrase due to its handy abbreviation -- SLA; also, it is duly supported by relevant theories.  

However, as a researcher and language educator I prefer the expression "to learn a language" as a more apt and precise desription of the process. Also, I try to avoid using the verb "acquisition" in relation to language learning.    

There is no consensus. Many schools of thought exits. Those who believe in the skills-building hypothesis advocate that languages are learned by for example memorizing rules in grammar. Traditional language instruction is mostly based on this view. This is world-wide.

Other researchers advocate that languages are acquired by exposure to comprehensible in put as in reading a novel, listening to a radio, or viewing a movie. This is a popular view in second language education.

There is also the comprehensible output hypothesis, which claims that output for example by speech, advances language acquisition. 

The list is long and the rivalry is endless.

It appears to me that each school of thought emphasizes an important aspect of language education. I hope that one day, there will be a comprehensive (united, generalized, or holistic) model of language education. 

Alphonse Furuma sums it up well, I wanted to add:

When we learn a language other than our native language as children, the part of the brain which lights up is the same for native and the other language.

When we learn another language, say past the age of 13-14, a different area lights up in our brain when we use L2 than the area which lights up when the native language is used.

Also, studies done looking at feral children might be helpful, and accidents which affect cognition.

If we accept the distinction between conscious learning and subconscious acquisition, (but not necessarily in the terms which it is discussed by Krashen), I would say from my own experience that adults with a lot of exposure to a foreign language both learn and acquire the language in question. 

They learn by receiving classes or by consciously reflecting on the language that they hear and read, and comparing it to their L1. However, they also acquire lexis, grammar, discourse features etc unconsciously. Let me give one example: Spanish people tell me that I now use the subjunctive correctly on all occasions. (Hardly a great feat given that I’ve lived in Spain for more than twenty years!) The rules in grammar books certainly helped me initially with the basic distinctions between the subjunctive and the indicative in Spanish. However, I soon found that no book ( and I bought around twenty in my pathological quest to perfect this area) gave me all the answers. So I must have picked it up naturally by hearing and reading the language.

 Students who do not live in the country where the language is spoken are likely to rely more heavily on learning. However, they too can acquire some language naturally by taking advantage of the opportunity to use the language outside the classroom ( reading novels, listening to podcasts, participating in forums etc).

To Alphonse regarding: "I hope that one day, there will be a comprehensive (united, generalized, or holistic) model of language education. "

There may never be a perfect or completely comprehensive model. However, one way round this is to practise informed eclecticism; reaching an understanding of different models, then taking elements from each of them and applying them to our teaching context with whatever adaptations are necessary. Given your answer, I would not be at all surprised if you were an informed eclectic yourself.

Nad Sy,

Language education leads from neurolinguistics are fascinating. However, the challenge for researchers is the complexity of the subject and research difficulties. We know so little about so many unanswered questions.   

To my view both instances are possible though it may largely depend on personal interests and needs be them of social, education or personal.

Hi,

I totally agree with José. All depends on the learnes´s learning styles and the proper environment  for acquisition, either natural or created. 

Dear all, 

Thank you for your explanations and point of views. Greatly appreciated. 

 As adult L2 learners, do we acquire or learn a language? Adults have both options open to them. Traditional methods of learning L2 dissect the foreign language into individual components and teach reading, listening and speaking separately. According to the Learning Pyramid, it represents conscious Passive Learning. As a result, learners continue thinking in the native language when trying to speak in English. The failure rate of learning L2 is very high.

Acquisition of L2 is a much better alternative because it is basically subconscious training of English skills. Dr. Krashen described the acquisition method: “Language acquisition is a subconscious process; language acquirers are not usually aware of the fact that they are acquiring language, but are only aware of the fact that they are using the language for communication.”

The problem is that very few teachers are trained to use acquisition method, besides there are no mobile applications or books for self-study which would be based on acquisition concept. This explains our current situation with foreign languages in the world.

To become fluent in L2 you should understand that the main barrier is your innate habit of thinking in the native language. You should stop thinking in your native language, and to achieve your goal of thinking in L2 you should use exclusively the patented acquisition method as described at www.lbtechnology.net .

Active Learning of English skills described on this website helps to unlearn the habit of cross-translating and acquire a new habit of thinking in L2 and speaking fluently. If you perform three actions at the same time- reading, listening and speaking – the habit of cross-translating is turned off automatically. This is a new type of comprehensible input for the acquisition of L2 skills, and you don’t need a teacher to achieve your goal! You need a smartphone or a tablet and Android application that provides an environment for training English skills and thinking in English.  

Based on the discussion going on, what I learned is ..... physically speaking, brains to learn/acquire a language are different in child and adult. It means child learning the first language (s) lean/acquire the language differently to how adults learn/acquire the language. But pedagogically speaking children and adults learn and acquire the language similarly, consciously and subconsciously.  

Nad Sy,

any literature references to the different parts of the brain lighting up when learning L1 and L2 in small children and teenagers? That'd be really helpful.

Dear researcher,

In brief adults learn L2, whereas children under the age of 14 [boys] and 15 [girls] acquire up to four or five languages.

This is really only a matter of definitions of words.  "Acquisition" means to obtain possession of something.  In terms of language, that means to achieve the capability to use the language at whatever level is required.

How does one achieve this capability?  By learning, of course.  But this learning may be natural and organic, or structured and intentional.  

Basically, learning is a conscious process, and it is used for L2 learning as instruction and conscious attention/effort are needed

Acquiring mostly refer to L1 for which no instruction is needed and the language competency is believed to be activated in the environment without any conscious effort or instruction. 

I agree - I have studied German, French, Spanish and Russian and am certified and have taught three of those languages in grades 7-12 for the past 17 years. I don't like the distinction  - not sure there is a clear one - between 'acquisition' and 'learning' a language. As adult learners (age 14+), our brains learn language differently than at younger ages. This is not necessarily a negative, as some try to make it out to be. I didn't start my study of languages until the age of 14 (9th grade in high school). But I am frequently mistaken by Germans in Germany for a native speaker of the language. This after 6 years of classroom study and then as an exchange student in Germany for 11 months during my senior year of college. I have not reached that level of fluency in any of the other languages I have studied, but if I devote the same time and energy to them as I have to German, I believe I could also attain / acquire those languages also to that level. What is required is dedication and persistance  . . . there is no magic and there are no shortcuts.

Dear friend,

In my opinion, in majority of the cases, Knowledge comes through Learning and skills come through acquiring. Hence, in my view speaking in any language is a skill so most of the cases, we can acquire the language rather than learning.

With regards,

Pavani Sasidhar.A

 Acquisition is a natural process happened unintentionally so it applies either with little learners in the same way they learn their first language or by actual interaction in authentic context. Learning on the other hand needs systematic institutions that supposed to be the place of learning process like schools for example. 

Liqaa

hi. It depends. some adults expose themselves to authentic language like films, music, emails, chatting with native speakers. they do not learn English; they have a kind of immersion program. the difference is blurred nowadays. learners as EFL can acquire language by communicating with native speakers a lot . best

Second language learning in adults may happen in a naturalistic or formal classroom setting. A naturalistic way would be within a target language speech community although this is usually rare. More commonly seen is learning in a formal classroom setting. Adults usually receive explicit instructions and less input while children tend to receive more “enjoyable” language activities

Please look at pending file:

As a teacher of Applied Linguistics I can say that adults learn and aquire at the same time espesially for a language if they want to master it they simply do intentionally-like reading novels - or unintentionally- like chatting with fluent natives .Thus ,they are able to do both.

If "acquisition" means to attain ability as a native, I think many adult learners can only learn a language, they can become fluent too, but not as same as natives. I am a language learner and I am pretty sure that I have both instrumental and integrative motivation. I am also aware that I will not become such native-fluent.