The main claim of this paper is that punctuation marks, in conjunction with spaces between words, function to provide visual rather than auditory cues for information structure in written English. INFORMATION STRUCTURE is defined here as dividing the flow of discourse into units, each containing a newsworthy element, and in contrast to the Systemic Functional systems of REFERENCE and THEME. A model of how these three systems interact is further supported by evidence from the historical development of reading and modern studies of the process of fluent silent reading. Reading silently does not require physical articulation and so written text is constrained by the saccading eye rather than the need to draw breath. The silent reader uses punctuation marks as a guide in a saccade to focus on the end of a clause which provides a non-arbitrary location for New information.Keywords: Punctuation, Information structure, Theme, Reference, Systemic Functional Linguistics, Embodiment Introduction Punctuation has vexed many writers past and present (e.g. Lowth, 1762;Truss, 2003). Surveys of the development of punctuation (e.g. Baron, 2001;Bruthiaux, 1993) reveal the longstanding divide between those that prescribe punctuation by prosodic principle and those that promote punctuation as the route to clarifying grammatical structure. This paper attempts to find a path through this apparent impasse by proposing not only that prosody and punctuation both realise the same function -that of information structure -but that they do so in a natural relationship to the spoken and written modes of language, respectively.The following section appraises a range of opinions on the topic of punctuation to reveal the contrast between punctuation by prosody and punctuation by grammar in written English. The next section examines the function and realisation of INFORMATION STRUCTURE within Systemic Functional Linguistics (SFL), contrasting it with the systems of REFERENCE and THEME, and culminating in a model of how the three systems contribute to written text. The paper then attempts to provide explanations for the difference in the realisation of INFORMATION STRUCTURE between spoken and written English, investigating firstly important steps in the historical development of written English, and then examining current understanding of the process of silent reading. The discussion aims to reveal how texts