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Second Language Acquisition: Accuracy, Fluency and Complexity

What is meant by accuracy in second or foreign language acquisition, and how does it relate to fluency and complexity?

What is meant by accuracy in second or foreign language acquisition, and how does it relate to fluency and complexity?

What Is Accuracy in Second Language Acquisition?

When a learner tries to use a second or foreign language, “accuracy” is the degree to which their usage follows the correct structures. More often than not the measurement is taken to imply accurate grammatical use. For example, “I not go” would be considered grammatically inaccurate even though we could derive intended meaning.

Accuracy can also be applied to the use of vocabulary by second language learners. For example, “I play skiing” is inaccurate because of the learner’s decision to use the word ‘play’ as opposed to ‘go’.

Similarly, choices of pronunciation used by the learner are evidence of inaccuracy. For example, second language learners often use “won’t” when they mean “want” and vice versa.

These inaccuracies in the use of grammar, choice of vocabulary and pronunciation make accuracy quite easy for a teacher to measure a learner’s progress and as such are often used in various assessments.

Accuracy in second language acquisition

Accuracy in second language acquisition

Fluency and Complexity in Second Language Acquisition

Accuracy is not the only measure of proficiency in a foreign or second language. Consider activities where spontaneous verbal responses are elicited by the teacher. The teacher is looking for understanding and the ability to communicate effectively. This ability to be spontaneously communicative is called “fluency”. One of the first academics to make this distinction between fluency and accuracy was Brumfit in the 1980s. Fluency is essentially how fast a learner can access and use the language in a well-paced smooth manner without awkward pauses.


In the 1990s, theorists began considering how elaborate and varied a learner’s use of language was. This dimension is called “complexity”. It is though a somewhat ambiguous and little understood concept. Theorists suggest there are two types of complexity: Cognitive and linguistic. Cognitive complexity is relative to and from the perspective of the individual learner (including for example their ability to remember, their aptitude and their motivation for learning). Linguistic complexity refers to the structures and features of the particular language.


Thus, the three components of second or foreign language learner acquisition are often viewed as this triangulation of accuracy, fluency and complexity (often abbreviated to CAF).

Complexity, Accuracy, Fluency (CAF): The constructs of language learner performance and proficiency

Complexity, Accuracy, Fluency (CAF): The constructs of language learner performance and proficiency

The Interrelationships Between Accuracy, Fluency and Complexity

Researchers have found that accuracy and complexity are linked in so far as they represent the level of internalized foreign language knowledge of the learner. Their knowledge is the scope of what they can draw on to form the language. Fluency, by contrast, is how much control and how fast the learner can access this knowledge. It is possible for a learner to be both fluent and accurate, but if the language they use consists of only simple structures then we cannot really say their use is complex (or advanced).

It has been argued (Ellis 1994) that if a learner develops more fluency, it may be at the expense of accuracy and complexity. I’ve seen this with students, usually in those with bold and outgoing personalities. They are not scared to try and they speak out. Consequently, they learn to communicate and draw quickly on their knowledge but it’s at the expense of the development of their grammar use. Nonetheless, I feel that those kinds of students do increase the complexity of their language use over time as they try to bring in new and more complex ideas. It is said though that how a student acquires knowledge is a different mental process to how they use it, so perhaps these outgoing students may be stunted when it comes to receiving new or complex information as opposed to actually using their existing knowledge. Meanwhile you may have students that are not willing to speak at all. Their anxiety about learning the language or propensity to focus too much on accuracy may hold them back when it comes to communication and fluency and indeed can block out their ability to take on new learning concepts.

If you are a teacher, have you ever got frustrated when you correct a student’s written work only for the final draft from the student to still come back with errors? Hatch (1979) discovered that foreign language learners don’t necessarily focus on the same kinds of correction that a teacher does. We might expect the student to focus on the accuracy side, the grammar, but in fact students tend to be concerned with minor details like the use of vocabulary or an improvement in what they are trying to communicate. Similarly, with regard to students working on developing their speaking skills, a teacher may be focusing on accuracy and pronunciation whereas the students could well be concentrating on how well they are getting their message across and what lexical choices they are making in order to achieve this.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Questions & Answers

Question: How could these three language development components (complexity, accuracy, and fluency) be measured? What is the theory of language learning behind these concepts?

Answer: A person’s ability to communicate in a foreign or second language has four elements: Accuracy (grammatical correctness), sociolinguistics (context of the language to the world around them), discourse (ability to authoritatively about a topic) and strategic competence (ability to get your meaning across to another person). The most commonly assessed of these areas would be accuracy (grammar) which can be assessed through the four skills of reading, writing, listening and speaking.

Grammatical competence itself has three components: Form and syntax (how the words are made and how they are strung together), meaning (the message the grammar is intended to give), and pragmatism (implied meaning). Assessment is typically done through such tests as sentence unscrambling, fill-in-the-blanks, error detection, sentence completion, picture description, elicited imitation, judging grammatical correctness in student's written work (probably the best way), and cloze passages (Larsen-Freeman, 2009). However, these kinds of tests do not get to whether students can actually use grammar in real-life situations. That’s where the communicative approach comes in by assessing through the creation of texts and face to face listening and speaking time. When a teacher interviews or listens to a student they can use scales to measure accuracy and complexity but these are judgment calls on the part of the teacher so the possibility of inconsistency is higher (McNamara and Roever, 2006).