This dissertation investigates the contextual factors that affect the understanding and interpretation of one Japanese topicalized construction, NP[subscript 1] wa NP[subscript 2] da sentences, by native speakers of Japanese. The construction allows two possibilities in the relation between the NP[subscript 1] and the NP[subscript 2]. When the two NPs are not syntactically connected (Type I), the sentence is generally vague, and a particular context is required to specify the meaning. When they are syntactically connected (Type II), they can refer to a semantically identical referent, and the sentence is naturally interpreted as an identity sentence. The aim of the study is to examine how context determines the meaning of Type I and Type II NP[subscript 1] "wa" NP[subscript 2] "da" sentences. These sentences were examined in a set of controlled experimental contexts by two kinds of test: Understandability and Interpretation. Results showed that readers generally tried to connect the NP[subscript 1] "wa" NP[subscript 2] "da" sentences to the context syntactically, semantically, or pragmatically when the sentences were presented in a context. Specifically, a syntactic and semantic relation with a particular verb in the preceding context sentence and the NP[subscript 2] or information about a particular place presented by a locative frame enhanced the comprehension of Type I NP[subscript 1] "wa" NP[subscript 2] "da" sentences. When these contextual factors were presented consistently and appropriately, Type II NP[subscript 1] "wa" NP[subscript 2] "da" sentences could be interpreted as non-identity sentences. When such context was not available, the interpretations tended to depend on the sentence-internal conceptual connection between the NP[subscript 1] and the NP[subscript 2] in both types of NP[subscript 1] "wa" NP[subscript 2] "da" sentences. These results suggest the reader's use of their linguistic and pragmatic knowledge differs according to the context and sentence type. The results also reveal a new understanding of the "aboutness" relation, a notion that accounts for the non-syntactic connections between the topic and the predicate. Specifically, in the process of understanding NP[subscript 1] "wa" NP[subscript 2] "da" sentences, establishing an "aboutness" relation refers to the process of finding an appropriate predicate in the context to create a proposition to connect the predicate (NP[subscript 2]) to the topic NP (NP[subscript 1]). [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]