By Prayag Patel, Spring 2025.

Learning a new language is no easy task: it takes time to memorize new vocabulary, comprehend foreign terms and phrases when reading or listening, and construct meaningful, intelligible, grammatically correct sentences. When tackling such a daunting task, it is natural to wonder: what is the optimal way to learn a new language? Linguists have been exploring this question for decades, and they have developed several theories about second language acquisition. Two influential theories are the Input Hypothesis and the Output Hypothesis.

In the 1980s, as a part of a more comprehensive theory of second language acquisition, linguist Stephen Krashen developed the Input Hypothesis, which stresses that learners should immerse themselves in the language they want to learn, also called their target language. In particular, Krashen argues that taking in comprehensible input—which involves reading or listening to material in the target language that is slightly above the learner’s current level—allows learners to use context clues to piece together the meaning of unfamiliar words [1].

Take, for example, the following simple German sentences: Das ist Mr. Spock. Mr. Spock hat zwei ohren [2]. Learners can start to find some meaning in these statements by recognizing the name, Mr. Spock. Moreover, learners can make their target language more comprehensible with the help of visual aids. If the German sentences are accompanied by the following image (see Figure 1), learners may figure out what “zwei” or “ohren” means. With enough scaffolding, learners can piece together an accurate translation: “This is Mr. Spock. Mr. Spock has two ears.” Krashen claims that by making it easier to understand messages in the target language, comprehensible input is necessary to acquire a new language.

Figure 1: Krashen pointing at Mr. Spock’s ears while saying “ohren” to make the German message more comprehensible. [2]

However, comprehensible input may not be enough. Linguist Merrill Swain suggests an opposing approach: focusing on producing output in the target language. After noticing how some advanced French immersion students failed to articulate their thoughts in French despite receiving a lot of comprehensible input, she developed the Output Hypothesis [3]. This approach forces learners to grapple with the structures of their target language. Since producing output requires more cognitive resources, learners must engage with their target language on a deeper level. Additionally, deliberate speech and writing allow learners to notice gaps in their linguistic knowledge and address them. By encouraging learners to wrestle with grammar and fill in linguistic gaps, Swain argues that output is necessary to acquire language on a deeper level. 

So, which approach is more promising? The answer is not so clear-cut. Both are crucial to second language acquisition. One cannot learn a language without some linguistic input [4]. However, output complements the knowledge gained by input. Producing linguistic output can help learners acquire the necessary grammatical tools of their target language to communicate their thoughts coherently. Indeed, studies comparing input-based learning and output-based learning have found that both methods can be used to build vocabulary and language competence [5,6]. 

In general, whether a learner chooses an input-based approach, an output-based approach, or a mix of both, it is important that they enjoy their learning. The Affective Filter Hypothesis suggests that emotions can influence language acquisition. Feeling overly stressed or unmotivated can hinder learners’ absorption of language input [7]. Similarly, feeling anxious about using the target language can impede learners’ ability to produce their language. So whether learners are focusing on speaking, listening, reading, or writing, they can set themselves up for success by creating a calm, stress-free learning environment and by simply enjoying the process.

[1] Krashen, Stephen D. 1982. “Principles and Practice in Second Language Acquisition.” https://www.sdkrashen.com/content/books/principles_and_practice.pdf.

[2] Krashen, Stephen D. “Language Acquisition and Comprehensible Input.” Posted January 28, 2016, by Tarek Hamza. YouTube, 15:25. https://www.youtube.com/watch?v=fnUc_W3xE1w.

[3] Pannell, Justin, Friederike Partsch, and Nicholas Fuller. 2017. “The Output Hypothesis: From theory to practice.” TESOL Working Paper Series 15, 126-59. https://www.hpu.edu/research-publications/tesol-working-papers/2017/2017-new-with-metadata/06pannellpartschfuller_output.pdf.

[4] Bahrani, Taher, and Rahmatallah Soltani. 2012. “Language Input and Second Language Acquisition.” Journal of Education and Practice 3, no. 3: 39-42. https://www.iiste.org/Journals/index.php/JEP/article/viewFile/1158/1079. 

[5] Nmaziandost, Ehsan, Elham S. Dehkordi, and Sajad Shafiee. 2019. “Comparing the effectiveness of input-based and output-based activities on productive knowledge of vocabulary among pre-intermediate EFL learners.” Asian-Pacific Journal of Second and Foreign Language Education 4, no. 2 (January). https://doi.org/10.1186/s40862-019-0065-7. 

[6] Trinh, Lien T. 2021. “The Roles of Language Input and Output in Second Language Acquisition–Discussions and Pedalogical Implications for EFL Teachers.” American Journal of Humanities and Social Sciences Research (AJHSSR) 5, no. 9 (October): 289-93. https://www.researchgate.net/publication/355060043_The_Roles_of_Language_Input_and_Output_in_Second_Language_Acquisition_-Discussions_and_Pedagogical_Implications_for_EFL_Teachers. 

[7] Ashtari, Nooshan. 2024. “Output Filter vs. Input Filter: What are They?” Language and Language Teaching 13, no. 25 (January): 120-22. https://llt.org.in/wp-content/uploads/2024/05/Output-Filter-vs-Input-Filter-Issue-25.pdf