The article is devoted to the English clauses of the syntactic structure NVasN, where the preposition as generally means 'in the capacity of', e.g., That effort was seen as a good idea. The aim of this research is to bring to light syntactic, semantic and pragmatic features of the constructions in question. According to the classification of Russian equality sentences proposed by I.B. Shatunovsky, English as-constructions of this type can be categorized as equality sentences based on common distinctive features shared by the nouns used. As far as the diachronic development of this construction is concerned, as is an amalgamated compound which derives from ealswa, where eal is the ancestor of all, while swa is the ancestor of so, hence the meaning 'being altogether alike'. It is generally believed that the preposition as was used in comparison structures (e.g. humble as a dove) until the 13th century. Later on, due to the process of grammatical constructionalization, the lexeme as came to be used as a predicative marker, thus giving rise to the internalization process in these constructions, which means that as could be applied in a greater number of contexts, most importantly, in those with mental representation and communication verbs (know, remember, think, consider, etc.). The main syntactic property of this construction is secondary predication. The authors analyze the predicative relation between the subject N and the predicative complement asN using examples from the Nature journal and some fiction texts, namely, H. Fielding's novel Bridget Jones's Diary, which allows the pragmatic potential of these constructions to be evaluated in two functional styles. It is stated that these relations can be either 'essential' or 'similative'. The 'essential' type denotes an objective, factual relation (semantic relations of inclusion or hyper-hyponymic relations; the relations 'object-function', 'subject-profession/age/nationality', etc.). The quality or feature encoded by the predicative complement is construed as being true, as being an actual characteristic. These sentences serve as models of cognitive processes and are typical of scientific prose, because the information presented in such kinds of texts is required to be objective. The verbs that are generally used here are mental representation verbs (e.g. know, view, classify, identify, interpret, etc.). The Passive Voice is the preferred form of the verb in these contexts. These constructions can be paraphrased with the copula be. The second type (similative use) denotes the relation in which the subject N and the predicative complement asN are compared, and the clauses can be paraphrased using the verbs look or seem. These sentences create an image, express subjective characteristics, some impressions and may serve as a means of self-presentation. These are typical of fiction texts. When combined with verbs of evaluation (e.g. laugh, ridicule), the predicative complement asN can also denote cause or purpose.