日常生活中，我們對語言和現實之間關係的認知，往往僅止於「現實世界裡的語言多半僅用來命名，或是指涉。」只有在某種情況下，我們才會毫不猶豫的承認，其實也有例外的時候，例如被用來創造藝術。在這種情況下，創作者通常擁有所謂的「破格」權力，以方便能用語言描述虛構的世界。然而，我們又會發現語言描述的現實，並不是我們熟知的現實；而語言的文本也不屬於我們通常被允許擁有破格特權的那種類型的文本。這種類型的文本正是史料，而這類史學家正如修昔底德。從古至今，修昔底德的語言運用，吸引了無數研究者的探討。這篇論文試圖利用系統功能語言學的理論，來解釋此矛盾的現象。根據這個理論，語言是一種記號系統，在其他更大、取決於社會的記號系統（例如：情境背景、文化、意識形態背景）的約束下來產生意義。這篇論文指出了解這些額外層面的意義，有助我們解釋修昔底德在文本中所做的選擇以及他如此選擇的理由，以及古今學者對修昔底德的作品做出不同詮釋背後的動機。

Our everyday understanding of the relationship between language and reality is that there is a real world which language most of the time simply “names” or designates; the only exceptions we are prepared to admit without much hesitation are instances in which language is employed as a means for the production of creative artefacts. In these cases we grant a “poetic licence” to the individual concerned, so as to allow him to engage in the description of a fictional world. Disturbingly, sometimes we find language that “does not” describe the reality we know in texts that “do not” belong to the categories we would ordinarily grant with a “poetic licence”. Such a category is historiography, and such a historian is Thucydides, whose use of language has attracted attention all the way from antiquity down to the present time. This paper attempts to explain this paradox with reference to the theory of language proposed by systemic functional linguistics. According to this theory, language is a semiological system that produces meaning under the constraints imposed by other wider and socially determined semiological systems (the Context of Situation, the Context of Culture, and Ideology). The paper examines how an understanding of these additional strata of meaning can help us explain not only the choices that Thucydides makes in his text, but also the reasons influencing his choices, as well as the motivations behind the differing interpretations of ancient and modern scholars to his work.