Emacs comes with numerous default keybindings, which inevitably conflict with system-level shortcuts. For Emacs beginners, resolving these conflicts can be a significant challenge.

One of the most common conflicts is with the command set-mark-command, which default binding is C-SPC~(Ctrl+Space)1. On Windows, Ctrl+Space is often used to toggle between English and Chinese input methods, which can makeCtrl+Space unusable for marking in Emacs.

To resolve this issue, you can either use the alternative binding forset-mark-command, C-@, or disable the Ctrl+Space functionality in Windows. Additionally, since the spacebar can be operated easily with either thumb, there is a “third option”: you can configure the Ctrl+Space so that one side Ctrl+Space is reserved for Windows, while the other side Ctrl+Space is available for Emacs or other applications. This is the solution I adopted because it allows me to maintain my habit of using both thumbs for operation.

In the latest version of Windows 11, you can achieve this as follows:

  1. Go to Settings > Time & Language > Language & region > Options > Microsoft Pinyin > Keys, and uncheck the Ctrl + Space box while leaving Shift checked.

  2. Open PowerToys (install it if you don’t already have it). In the Keyboard Manager section, add a key remapping: map Ctrl(Left) + Space to Shift orWin(Left) + Space.

For older versions of Windows, where there’s a UI bug preventing such changes 2, you can solve this by manually editing the registry:

  1. Navigate to HKEY_CURRENT_USER\Control Panel\Input Method\Hot Keys\00000010. Modify the value of Key Modifiers to 02 80 00 00, or 02 40 00 00 3.
  2. If you want to apply this change for all new users, make the same modification under HKEY_USERS\.DEFAULT\Control Panel\Input Method\Hot Keys\00000010.

After making these changes, restart your computer to take effect.

It seems that only Ctrl+Space can be “split,” as other key combinations are naturally easier to reach with one hand. For example, Ctrl+a inherently impliesRight Ctrl+a.

  1. Emacs uses unique convention for keybinngs, where C-SPC is shorthand forCtrl+Space. This article adopts the common convention for now. ↩︎

  2. https://superuser.com/questions/327479/ctrl-space-always-toggles-chinese-ime-windows-7 ↩︎

  3. 02 indicates Ctrl, 80 indicates the left side, and 40 indicates the right side.https://learn.microsoft.com/en-us/windows/win32/tsf/tf-mod--constants ↩︎