Grammatical knowledge is important in both second language acquisition and learning, because grammar reveals how language works. Grammar (cited in Lynch in http://www.elbase.com) is a branch of linguistics dealing with the form and structure of the words or morphology, and their interrelations in sentences, called syntax. Thus, grammatical knowledge is a form and structure of words and their interrelation in sentences. .
According to Anderson in Mitchell (2004), the grammatical knowledge is divided into two forms, namely declarative grammatical knowledge and procedural grammatical knowledge. Declarative knowledge (explicit knowledge) is the knowledge about something, which is factual information and is usually conscious: for instance, knowing the capital of the U.S. is Washington D.C. (Dekeyser 2001, in Akira, 2002). Besides, procedural knowledge (implicit knowledge) is the knowledge of how to do something and is usually unconscious, for instance, riding a bicycle. On the other hand, Akira (2002) defines declarative grammatical knowledge as the knowledge about grammar rules, while procedural grammatical rules is the knowledge about how to use grammar rules appropriately, meaningfully and automatically. .
In second language acquisition, having a good grammatical knowledge is very crucial. Grammatical knowledge can be acquired effectively by understanding all aspect of language such as phonology, vocabulary, morphology, syntax and discourse. As stated by Seville-Troike (2006), phonology refers to the sound system of the words. By understanding this aspect, learners can differentiate speech sounds that make a difference in meaning, syllables structure, intonation pattern, and rhythmic patterns. While vocabulary or lexicon related to word meaning, pronunciation, grammatical category (part of speech), and possible occurrence in combination with other words and idioms. Having good understanding in morphology can guide learners to understand morphemes, inflections that carry grammatical information, prefixes and suffixes.