Some learners in articles pointed out that a pithy statement that without grammar, a lot of things could not be expressed. However, without vocabulary, nothing could be expressed.

Schmitt thought that to fully describe a person's level of vocabulary knowledge should be at least from three angles to consider. First is the breadth. Second is the depth. Third is the automaticity of the vocabulary knowledge application.

Some learners believed that the biggest obstacle for the second language vocabulary learners in reading is not the lack of reading strategies but the lack of vocabulary. Some learners pointed out that in the foreign language environment, the English learners should not only have a sufficiently large vocabulary size but also to master the vocabulary depth and master the response speed to obtain the understanding easily and accurate. In recent years, the focus of the study of vocabulary has from the vocabulary size or vocabulary breadth to the study of vocabulary depth. They also draw on previous studies(Richards, 1976; Nation, 1990). In their paper, it attempts to explore the relationship between the vocabulary knowledge including the vocabulary breadth knowledge and the vocabulary depth knowledge and reading comprehension. The results not only confirmed the importance of vocabulary in reading, but also proved the significance of vocabulary depth in reading. The high correlation between the vocabulary depth and the vocabulary test results further confirms that these two levels is interrelated and mutually influenced. The expression among the vocabulary breadth, the vocabulary depth and the reading is as follows. The rich knowledge of vocabulary formation can make more vocabulary family members entered the lexicon to enlarge the vocabulary size. The rich vocabulary can enable us to be more description, explanation the meaning and collocation. The results of regression analysis show that the vocabulary size and the depth of vocabulary can predict the reading performance.来!自~优尔论-文|网www.youerw.com

2.2 Definition of breadth and depth of vocabulary

The collection of the words in a language is called vocabulary which is used in different senses. In the paper of "The role of vocabulary teaching," written by Richards published in 1976, the definition of vocabulary had been presented firstly. He also firstly presented that if one vocabulary is mastered, the different aspects of vocabulary knowledge should be learned. 

The vocabulary knowledge includes two aspects, that is, the vocabulary breadth and vocabularydepth. The vocabulary breadth is defined as the number of the vocabulary, which is the number of the vocabulary that the students at least have a superficial understanding of its meaning. The vocabulary depth is defined as the layers of understanding for the vocabulary.

Because the vocabulary knowledge is an extremely complex system, so far, the nature of the vocabulary knowledge has not yet reached a unified, undisputed consensus. On the concept and connotation of vocabulary knowledge, the second vocabulary researchers have risen different but complementary theoretical framework, however, most researchers believe that vocabulary knowledge is not one-dimensional, but complex and multi-dimensional.