The purpose of this paper is to analyze the semantic structure of the three types of English articles—indefinite, definite, zero articles―with respect to the supposedly flexible boundaries of English nouns under the framework of Cognitive Grammar (Langacker 1987, 1991a, 1991b, 2000). To facilitate this, a new notion has been proposed: Boundedness Filter (BF), which is thought to play a decisive role in determining the activation or inactivation of noun boundaries in relation with the selection of corresponding articles. BF is supposed to operate in a variety of cognitive domains such as physical space for the indefinite article and psychological space for the definite article. This paper further claims that the count or mass-like property of a given noun is not fixed originally as prescribed in dictionaries or grammar books; rather, its boundary has a flexible feature depending upon the context in which it is used. This is why a common noun with its indefinite article as a boundary marker can sometimes be changed into a mass noun without any article. The BF and flexible characteristics of English noun boundaries can also be used to explain the reason that some apparently visible boundaries are not realized in physical space as indefinite articles.

Given an English sentence composed of a subject, its complement, and a copula (also called a linking verb), the question of choosing a right copula has been, from the standpoint of traditional grammar, a matter of idiomaticity rather than one of analysis and comprehension. This paper, under the framework of Cognitive Grammar (CG) (Langacker 1987, 1991, 2000, 2002), semantically analyzes the underlying mechanism in our brain which is supposed to operate in determining an appropriate copula. We will first consider two processes with regard to the choice of a subject and its complement: the narrowing-down of encyclopedic knowledge and the acting area of a subject for choosing its complements. After this pairing process between a subject and its complement, this paper proposes three cognitive parameters concerned with the right choice of a copula between the two selected items. Whether the chosen copula is appropriate or not will be filtered by restorability, desirability, and perfectiveness. By proposing and explaining those three cognitive parameters, this paper suggests that English copulas should also be learned by understanding the formation of meaning mechanism by us human beings' mental activities.