This book focuses on a hieroglyphic and hieratic peculiarity traditionally called "dissimilation graphique", but now labelled "dissemblance graphemique" (graphemic dissimilarity). Mostly attested in Old Kingdom texts, we can see this graphemic peculiarity in archaic duals and plurals, thus showing several classifiers (or determinatives) instead of a single one with diacritic strokes. A lexeme is "dissimilar" if its classifiers are distinct, and not identical as is usually the case. For example, mhy.t, "fish(es)" is written in a standard way if the three fishes used as classifiers are the same; but its writing is "dissimilar" if three species are figured, instead of a sole one. So, the present book aims at studying in a systematic way the occurrences of graphemic dissimilarity in Old Kingdom texts. Involved lemmas, used hieroglyphs, relevant categories... The grammatological and linguistic analysis shed new lights on a little studied peculiarity, thus offering a new approach for Ancient Egyptian categorization and Weltanschauung in general.