A recent article in the journal Second Language Research by Isabel Jensen, Roumyana Slabakova, Marit Westergaard, and Bjorn Lundquist (2018) lends support for a theory of second language acquisition called The Bottleneck Hypothesis.

The Bottleneck Hypothesis states that functional morphology poses the greatest obstacle to second language learners acquiring an L2, and, thereby constitutes a bottleneck of cognitive load, thereby limiting the rate of acquisition. The theory originates from a paper by Roumyana Slabakova (2014) of the University of Southampton, in which she posits a theory that syntax and semantics can be acquired more easily than functional morphology.

Image from Slabakova, 2014

Functional Morphology

In linguistics, morphology refers to the building blocks of words, with a morpheme indicating the smallest unit of meaning at the word level. In other words, the un- in unstoppable is a morpheme. So, functional morphology deals with syntax operating at the word, rather than sentence, level. For example, the -s attached to verbs with a singular present tense subject (“John walk-s to school” Or “He speak-s Spanish”) exemplifies morphological syntax.

Jensen et al.

The study by Jensen et al. examined sixty middle- and elementary-school Norwegian children regarding their performance on a standardized exam that tested subject/verb agreement (functional morphology) and word order (sentential syntax). All of the children were English L2 learners. The researchers sought to answer the following research questions:

Research Question 1: Is functional morphology more difficult than core syntax? […]

Research question 2: Is functional morphology a more persistent problem than core syntax? […]

Research question 3: Which syntactic and morphological sub-conditions are more difficult? […]

(Jensen et al., 2018)

They found the data favored all three propositions, and hence, supported Slabakova’s hypothesis (2018).

Slabakova suggested The Bottleneck Hypothesis poses significant implications regarding the need for a return to focus on form approaches to grammar teaching, particularly regarding those structures entailed by the functional morphology (2014).

For teachers who haven’t cracked open the literature for a spell, focus on form refers to explicit grammar instruction in the classroom, in either a preemptive (grammar lessons) or reactive (grammar corrections) capacity (Ellis, Basturkmen, & Loewen, 2001).

Implications for higher education ESL Classrooms

If we accept The Bottleneck Hypothesis as true, the implication that morphological features require more practice would justify greater emphasis not only on grammar, but on specific features of grammar that operate in the morphology, such as verb agreement and case marking. Furthermore, might such a proposition be more pertinent for learners whose L1s are morphologically impoverished, such as Mandarin Chinese? When one considers that the majority of English learners in America’s universities are from China, a theory like the Bottleneck Hypothesis could exert significant pedagogical influence.

However, it is worth noting that The Bottleneck Hypothesis lands solidly in the Chomskian minimalist program approach to universal grammar (UG) of language, and as such, is not likely to appeal to those who do not subscribe to UG arguments. So don’t expect any significant changes to pedagogical practice in the field without a preponderance of support.

Nevertheless, if you find The Bottleneck Hypothesis compelling, then perhaps it’s time to pull the dust covers off those audio-lingual drills.


Ellis, R., Basturkmen, H., & Loewen, S. (2001). Preemptive Focus on Form in the ESL Classroom. TESOL Quarterly, 35(3), 407–432. https://doi.org/10.2307/3588029

Jensen, I. N., Slabakova, R., Westergaard, M., & Lundquist, B. (2018). The Bottleneck Hypothesis in L2 acquisition: L1 Norwegian learners’ knowledge of syntax and morphology in L2 English. Second Language Research, 0267658318825067.

Slabakova, R. (2014). The bottleneck of second language acquisition. Foreign Language Teaching and Research46(4), 543-559.

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