A “sign” in Saussure’s terminology consists of a signification (a concept or idea) and a signal (the “sound pattern” associated with the idea). He suggests some analogies: “This unified duality has often been compared with that of the human being, comprising body and soul. But the parallel is unsatisfactory. A better one would be with chemical compounds, such as water. Water is a combination of hydrogen and oxygen: but taken separately neither element has any of the properties of water.”

One could extend the analogy: Words in sentences are like atoms, which take on different properties in combination with other words.