<p>The study investigated the independent contributions and relative importance of morphological, vocabulary, and syntactic knowledge to listening and reading comprehension among second language (L2) learners. A total of 608 participants were recruited and completed a battery of tests to measure morphological knowledge, vocabulary breadth, vocabulary depth, syntactic knowledge, listening, and reading comprehension. Hierarchical regression and dominance analysis were employed to determine the unique predictive power and relative importance of four core language constructs across listening and reading modalities. The analysis indicated that morphological, vocabulary, and syntactic knowledge each contributed unique variance to both listening and reading comprehension. A consistent hierarchy of predictive strength was observed for both modalities, with vocabulary breadth emerging as the strongest predictor, followed by syntactic knowledge and then morphological knowledge, while vocabulary depth demonstrated the weakest unique contribution. While listening and reading shared a common hierarchy of linguistic skills to build a coherent mental model, the cognitive routes for achieving comprehension were adaptively shaped by input modalities. The transient nature of auditory input may lead to an integrated processing mode in listening, with vocabulary breadth, syntactic and morphological knowledge potentially operating as a unified system under time constraints. However, the visual permanence of written text enabled a more analytical approach in reading, allowing morphological knowledge to function as a critical tool to support reading comprehension.</p>