The Unwanted Typography
macOS includes a system-wide text replacement feature designed to make typing faster and more visually appealing. One of its default behaviors is to automatically convert standard, plain-text fractions typed with a forward slash (like 1/2 or 1/4) into specialized, single-character fraction symbols (like ½ or ¼). While this looks elegant in a formal letter or recipe document, it is disastrous if you are typing mathematical equations, command-line arguments, or specific formatting codes where the literal numbers and the forward slash character are required syntax, as the OS will silently overwrite your input.
Disabling Symbol Substitution
To preserve your exact keystrokes and stop macOS from automatically correcting fractions and other specific typography, you must turn off the text replacement feature in the Keyboard settings.
This setting is handled globally, affecting almost all native Mac applications (like Mail, Notes, and Safari). Click the Apple logo in the top-left corner and select System Settings. In the left-hand sidebar, scroll down and select Keyboard. In the main panel, under the “Text Input” section, look for the “Input Sources” header and click the Edit… button next to it. A new dialogue window will appear. Toggle Off the switch for Use smart quotes and dashes, which often governs broader typographical replacements. However, to specifically stop fractions, you must also look at the Text Replacements… button (found back on the main Keyboard settings page). Click it to view the list of automatic substitutions. If you see rules forcing `1/2` to become `½`, click the rule to highlight it, and press the minus (-) button at the bottom of the window to delete the macro entirely.