This is a study with descriptive hypothesis-testing design investigating the true nature of L2 grammatical proficiency via focusing on its component parts. It examines the performance of 60 female EFL learners between 19 and 30 years of age at 2 proficiency levels using 2 types of computerized Grammaticality Judgement tasks in different orders (i.e. Explicit Written Task and Implicit Written Task) for each participant at a 1 week interval for 2 weeks per each task to determine the extent to which L2 learners' performances are affected by a few components of grammatical proficiency chosen and manipulated out of many others that exist (i.e. Implicit Knowledge, and Explicit knowledge) as well as language proficiency while focusing on subjacency. Participants rendered GJ tasks on a 2-point interval. Results from analyzing the elicited measurement data indicate that the performance scores of the two proficiency groups in the two Grammaticality Judgement tasks did not differ significantly.