Exotic and familiar mathematical symbols – 11/21/2023 – Marcelo Viana

Some mathematical symbols, like the square root (√) and infinity (∞), seem exotic and, I suspect, a little scary. Others have become as familiar as the letters of the Latin alphabet (A to Z) or the numerals (0 to 9) of Hindu-Arabic numerals.

This is the case, for example, with the addition (+) and subtraction (–) signs, or even the most important of all, the equals sign (=). However, these symbols are recent inventions, much more recent than Latin letters, which date back to the 6th century BC, or numerals, created in the 5th century AD.

The symbol = was first used in 1557 by the Welsh mathematician and physician Robert Recorde (1510–1558). In the book “The Whetstone of Witte”, in which he deals with various questions about whole numbers, fractions and irrational numbers, he explains convincingly. “And to avoid the tedious repetition of the words ‘is equal to’ I will use, as I usually do in my work, two parallel lines with the same length, that is =, as there are no two things that are more equal.”

In fact, Recorde’s parallels were much longer, but, over time, the symbol was shortened. Not that it was adopted immediately: in the 18th century it was still common to find the signs ║ or æ (initial of æqualis, “equal” in Latin) to signify equality. But Robert Recorde’s choice ended up prevailing, largely because it was adopted by Newton and Leibniz.

“The Sharpening Stone” was also the first work in the English language to use the signs + and –, but, in this case, Recorde was not the inventor: “there are two more widely used symbols, of which the first is written + and is better known, and the other is written – and is less known”, he explained.

In the 15th century, it was more common to use the letter p (from plus, “more” in Latin) or the word et (“and” in Latin) to represent addition: the + sign was an evolution of the latter, as the “e” was omitted, leaving only the “t”. The sign – is a deformation of the letter m, initial of minus, “less” in Latin.

A student and, later, professor at the universities of Oxford and Cambridge, Recorde later became a royal physician, during the reigns of King Edward 6^O and Queen Mary, in addition to directing the kingdom’s Mint. Sued for libel by a political enemy, he was imprisoned for debt and died in prison.

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