Displays have separate Spaces: on or off on your Mac?
There is one checkbox that decides how your Mac treats a second monitor, and almost nobody touches it deliberately. Displays have separate Spaces is either the reason each screen feels like its own workspace, or the reason you can't drag a window across the gap between them. It is on by default, changing it needs a log out, and one of the two settings will annoy you noticeably less than the other. Here is what each one actually does.
Where the setting lives, and what it defaults to
System Settings → Desktop & Dock, then scroll to the Mission Control group near the bottom. The toggle is the last one in that group.
It ships on. Under the hood it is the inverse of a preference
called spans-displays in com.apple.spaces — on means each display
gets its own Spaces, off means one Space spans them all — which is
why some guides describe the same setting backwards.
Whichever way you move it, the change does not apply until you log out and back in. If you flip it and nothing looks different, that's why. A restart works too; a Dock relaunch does not reliably.
Displays have separate Spaces: on vs off
| On (default) | Off | |
|---|---|---|
| Spaces | Each display has its own set | One Space stretches across every display |
| Switching desktops | Changes only the display you're on | Changes all displays at once |
| A window across the bezel | Confined to one display | Can sit half on each screen |
| Menu bar | On every display, active one lit | Main display only |
| Dock | Follows your pointer to any display | Main display only |
| Full screen | Other displays keep working | Other displays go blank |
| Split View / tiling on a second display | Works | Unavailable |
| Stage Manager | Works | Off, and can't be turned on |
| Mission Control | One overview per display | Both screens shown as one canvas |
The short version: on treats your monitors as two computers that share a keyboard. Off treats them as one very wide screen with a seam in it.
What actually breaks when you turn it off
This is the part the checkbox doesn't warn you about, and the reason "off" is a bigger decision than it looks.
- Stage Manager stops working entirely. Apple's own fix for "I can't turn Stage Manager on" is to go and turn separate Spaces back on. If you use it — or want the option — this setting is not available to you. (Stage Manager vs Mission Control covers whether it's worth it.)
- Split View goes with it, and macOS's own Move & Resize tiling commands grey out on the secondary display. If your tiling shortcuts suddenly stopped working, this setting being off is one of the usual causes.
- Full screen blanks your other monitor. Send a video call or an editor full screen and the second display goes to a plain background. For anyone who runs a reference window beside their main task, that alone settles it.
- The menu bar and Dock stop following you. Both live on the main display only, so half your reaching gets longer.
What you get in return is exactly one thing: a window can span both screens. That is a real need — a long timeline in a DAW or video editor, a wide spreadsheet, a single canvas that genuinely wants 6000 pixels. If that's your work, off is correct and the costs above are the price. If it isn't, you are trading four features for a capability you will use twice a year.
So: on or off?
Leave it on unless you can name the specific window you want to stretch across two monitors. That covers nearly everyone: developers, writers, anyone with a browser on one screen and a chat app on the other.
Turn it off if you edit audio or video, work in a CAD or DAW timeline, or use one app that is genuinely happier at double width — and accept that Stage Manager, Split View and full-screen-on-one-screen go away.
There is no third option, and no per-app override. It is one global choice.
How to change it
- Open System Settings → Desktop & Dock.
- Scroll to Mission Control.
- Toggle Displays have separate Spaces.
- Log out and back in (Apple menu → Log Out), or restart.
While you're in that pane, turn Automatically rearrange Spaces based on most recent use off. With it on, your desktops silently reorder themselves, so ⌃→ lands somewhere different each time — the single most disorienting default in the whole Spaces model. More on that in the Spaces and virtual desktops guide.
One live wrinkle worth knowing: since macOS Tahoe, people have reported the setting reading differently after an update than it did before. If your multi-monitor behaviour changed and you didn't change anything, check this toggle before you go hunting elsewhere.
After you've picked, the real problem is still navigation
Both settings leave the same gap. With separate Spaces on, each monitor is its own little world and you spend the day hunting for the window that is on the other one. With it off, you have one enormous canvas and windows land wherever there's room. Either way the friction isn't the setting — it's that macOS gives you no fast, keyboard-driven way to put a window where you want it or to jump to the one you're thinking of. (The multi-monitor productivity guide has the wider setup; the windows-resize-on-docking piece covers the other half of the plugging-in mess.)
That's the gap Let's Tile and Let's Switch fill, and neither is a Spaces feature — they work on windows, so your answer above doesn't change them.
Let's Tile is one shortcut instead of twenty. Press it, a grid drops over the window you're using, you steer with the arrow keys and press return. The free tier is a 3 × 2 grid — halves, thirds, two-thirds, quarters, full screen — and it stays free. Pro ($9.99, paid once) adds grids you define yourself, a different grid per display, remembered automatically, and throwing a window to your other display mid-tile, which is the multi-monitor move you'd otherwise do with a mouse.
Let's Switch answers the other half. Hold ⌥⇥ and you get a live
preview of every open window, most recent first, across all your
monitors — not just apps, which is as far as ⌘⇥ gets you.
Option-backtick (⌥` ) cycles one app's windows. Both free. Pro
($9.99) adds an ⌥Space search palette
for the days when you have too many windows to flip through at all.
No account, no subscription, no telemetry, up to 20 devices per key.
Frequently asked questions
Is Displays have separate Spaces on or off by default? On. macOS gives each display its own set of Spaces unless you deliberately change it.
Why is the setting greyed out or missing? It only appears when more than one display is connected and active. On a laptop with the lid closed and one external monitor, there's only one display, so it isn't shown.
Do I have to log out for it to take effect? Yes. This is one of the few macOS settings that genuinely needs a fresh login — logging out and back in is enough, no full restart required.
Why can't I turn Stage Manager on? Almost always because separate Spaces is off. Turn it on, log out and back in, and Stage Manager becomes available again.
Will turning it off let me tile a window across two monitors? It lets a window span the gap if you drag or resize it there. It doesn't give you a command that does it, and macOS's tiling shortcuts stop working on secondary displays in that mode.
Does it affect how full-screen apps behave? Substantially. With it on, one app going full screen leaves your other displays usable. With it off, they go blank until you leave full screen.