Grammarly for Mac automatically turns off the macOS standard spellchecker when it’s installed. If you prefer to keep your macOS spellchecker on, please follow these steps: 

  1. Open Finder and click Go. 
  2. Select Utilities and open Terminal.
  3. Paste the following command into the Terminal window, then press Enter:

    defaults write -g NSAllowContinuousSpellChecking -bool true

  4. Restart your computer for the change to take effect.