The present paper concerns the cognitive, cultural and rhetorical motivations behind idioms and proverbs. Our aim is to shed light on the presence of cultural markers in these phraseological and paremiological units. Working from some examples from English, French, German and Russian, we will analyze the driving forces underlying familiar idioms. How are idioms motivated? How did they appear and why do they exist? Are they grounded in cultural details or are they rather the result of semantic reinterpretation? The analysis will begin by defining the terms to be used in the paper: phraseological unit, collocation, idiom, formulae, culture, figurative and literal meaning, transparent and opaque images, motivation and semantic reinterpretation. First, transparent phraseological units will be confronted in the four languages studied. We will reflect upon the reasons for the existence of such similar idioms in different languages. Then, attention will be drawn to idioms referred to as opaque. What are the reasons for opacity? Is there any rule by which we might be able to predict the evolution of the idiom? Some conclusions will be drawn at the end.