Definition:Equals/Historical Note

Historical Note on Equals

The equals sign was introduced by Robert Recorde in his $1557$ work The Whetstone of Witte.

Placing two long hyphens together, one above the other, he wrote:

To avoide the tediouse repetition of these woordes: is equalle to: I will sette as I doe often in woorke use, a paire of paralleles, or gemowe lines of one lengthe: $= \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! = \!\!\! =$, bicause noe .2. thynges, can be moare equalle.

The word gemowe comes from the Latin geminus meaning twin.

François Viète used the symbol $\sim$, while René Descartes used $\propto$.

Both were in due course supplanted by $=$, a shortened and hence more efficient version of Recorde's invention.

It is suggested by some sources that this was mainly through the influence of Leibniz.

Sources

• 1992: George F. Simmons: Calculus Gems ... (previous) ... (next): Chapter $\text {A}.19$: Leibniz ($\text {1646}$ – $\text {1716}$)
• 1998: David Nelson: The Penguin Dictionary of Mathematics (2nd ed.) ... (previous) ... (next): equals sign
• 2008: David Nelson: The Penguin Dictionary of Mathematics (4th ed.) ... (previous) ... (next): equals sign
• 2008: Ian Stewart: Taming the Infinite ... (previous) ... (next): Chapter $4$: Lure of the Unknown: Algebraic symbolism
• 2009: Ian Stewart: Professor Stewart's Hoard of Mathematical Treasures: Who Invented the Equals Sign?