While without grammar, little can be conveyed; without vocabulary, nothing can be conveyed. If vocabulary is not more important than other aspects of a language, it is at least as important as the others.
Huckin and Bloch(1993) point out, “Research has shown that second-language readers rely heavily on vocabulary knowledge, and that a lack of vocabulary knowledge is the largest obstacle for second-language readers to overcome. Laufer and Sim(1985) list knowledge of vocabulary, subject matter, discourse markers and syntactic structure in order of decreasing importance in 2nd language reading ability.
In surveys of ESL students in intensive academic programs (Flaitz, 1998; James, 1996; Folse 2004), students expressed a strong desire for vocabulary instruction. In many surveys, students ranked vocabulary development second only to opportunities to speak in class.