When typing on your Mac, you are unable to use Shift + S to make a capital S letter. The Shift key works with other letters to make capitals and the S key types when pressed by itself.
The Shift+S keys may be assigned as a shortcut for Speech.
- Click the Apple icon in the top left of the screen.
- Click System Preferences.
- Click the Speech icon.
- Click the Text to Speech tab.
- Uncheck the option “Speak selected text when the key is pressed”.
Also, if you want to keep the option enabled, click “Set Key…” and set a new shortcut.