For more than a decade in the middle of the 20th century, chemists debated exactly what “carbocations”—molecules with a positively charged carbon atom—looked like. What is known as the “classical view,” which was taught at the beginning of that century, stated that the carbon in these molecules held the charge; the “non-classical view” held that the charge could also be shared by other nearby atoms. Both theory and experiment eventually proved that non-classical carbocations existed, and the debate faded away. Even if these structures exist, most chemists believed, they had no practical relevance.