If you need a clear, step‑by‑step guide to using the CTRL+SHIFT+I shortcut in AutoCAD, this article explains what the shortcut does, how to use it, why it sometimes fails, alternative methods to achieve the same result, troubleshooting tips, and a practical FAQ.
What is the Ctrl+Shift+I shortcut?
Ctrl+Shift+I in AutoCAD toggles Infer constraints on and off.
- Infer Constraints is the automatic detection and application of geometric constraints (like perpendicular, parallel, vertical, horizontal, concentric, tangent, coincident, collinear, etc.) while you draw or edit geometry.
- The setting behind this behavior is the system variable INFERCONSTRAINTS: when set to 1, AutoCAD will try to infer and apply constraints automatically; when 0, it will not.
This feature is part of AutoCAD’s Parametric tools (introduced in AutoCAD 2010 and present in versions with the Parametric workspace). Use it when you want AutoCAD to help build relationships between objects automatically; turn it off when inferred constraints get in the way of free editing.
How Infer Constraints works — quick explanation
- With Infer Constraints enabled, when you draw or Move objects, AutoCAD inspects geometry and adds geometric constraints where it detects logical relationships (for example, two lines that meet at a right angle may receive a Perpendicular constraint).
- These constraints become part of the geometry’s parametric definition, so changing one element can drive related elements predictably.
- Constraint symbols may appear in the drawing; display is controlled by the CONSTRAINTDISPLAY system variable (1 = show, 0 = hide).
How to use Ctrl+Shift+I (step by step)
Option A — Keyboard shortcut (fast)
- Open the drawing in AutoCAD.
- Press Ctrl+Shift+I once to toggle Infer Constraints on (or off).
- Draw or edit objects and observe whether constraints are being applied automatically.
Bold tip: If you don’t see expected behavior, check INFERCONSTRAINTS (see troubleshooting).
Option B — Using the ribbon (UI)
- Go to the Parametric tab on the ribbon.
- In the Manage Constraints or Infer Constraints area, click the Infer Constraints toggle button to enable or disable inference.
Option C — Command line (explicit)
- Type INFERCONSTRAINTS at the command line and press Enter.
- Enter 1 to enable or 0 to disable.
Example (before/after)
- Before (Infer off): draw two lines that meet — no constraint is created; you can move endpoints freely.
- After (Infer on): draw the same two lines — AutoCAD may apply a Perpendicular constraint automatically if the geometry indicates a right angle; moving one line will respect the inferred relationship unless you remove the constraint.
Alternatives to Ctrl+Shift+I
If you prefer manual control, or if the shortcut is not working, you can:
- Use the Parametric ribbon tools:
- Geometric constraints tools (select lines and apply Perpendicular, Parallel, Coincident, etc., manually).
- Dimensional constraints for size and distance relationships.
- Use the command line to set INFERCONSTRAINTS = 1 or 0 as described above.
- Add constraints manually with the GUI: Parametric > Geometric panel > pick the desired constraint tool and apply to selected geometry.
- Temporarily disable inference and then apply constraints manually to get exactly the relationships you want (recommended for precise parametric control).
Common reasons Ctrl+Shift+I doesn’t work and fixes
- Keyboard shortcut reassigned or disabled
- Fix: Open the CUI (Customize user interface) and verify that Ctrl+Shift+I is assigned to toggle INFERCONSTRAINTS. If not, reassign or create a shortcut key.
- INFERCONSTRAINTS is set but constraints don’t show
- Fix: Check CONSTRAINTDISPLAY — set it to 1 to display constraint symbols. Also ensure layer visibility isn’t hiding constraint objects.
- Running a workspace or profile without Parametric tools
- Fix: Switch to a workspace that includes the Parametric tab or enable Parametric tools from the ribbon customization.
- Conflicts with OS or other applications intercepting the key combination
- Fix: Test shortcut in a New drawing; close background apps that might intercept Ctrl+Shift+I (screen capture, hotkey utilities). Reboot if necessary.
- Custom LISP, script, or profile locking system variables
- Fix: Check startup LISP or scripts that set INFERCONSTRAINTS and modify or disable them. Reset AutoCAD profile to default and test.
- Older/limited product edition (some LT builds or version differences)
- Fix: Confirm your AutoCAD edition and version support Parametric constraints. If not supported, use manual constraint tools in versions where available or upgrade if needed.
Troubleshooting steps (quick checklist)
- Type INFERCONSTRAINTS and press Enter — set to 1 to enable.
- Ensure CONSTRAINTDISPLAY = 1 to show constraints.
- Switch to the Parametric tab and verify Infer Constraints toggle status.
- Check CUI for shortcut assignment if Ctrl+Shift+I does nothing.
- Disable background apps that may capture Ctrl+Shift+I.
- Test in a fresh drawing to rule out drawing-specific script or corruption.
- Reset AutoCAD profile if persistent odd behavior exists.
Practical tips and best practices
- Use Infer Constraints when sketching or building parametric models to speed up constraint creation, but turn it off for freeform drafting.
- When collaborating, be explicit about constraints: inferred constraints can differ between users and lead to unexpected behavior. Clean up unwanted constraints with the Delete Constraints or manual removal tools.
- Use CONSTRAINTDISPLAY to toggle visibility of constraint symbols (helps keep the drawing readable).
- Learn to add constraints manually (Parametric > Geometric) for fine control; inference is a convenience, not a replacement for deliberate parametric design.
- Periodically review constraints with Show/Hide Constraints tools to understand how geometry is constrained.
FAQ
What exactly does Infer Constraints do in AutoCAD?
Infer Constraints automatically detects geometric relationships between objects as you draw or edit and creates corresponding geometric constraints (perpendicular, parallel, coincident, etc.). It is controlled by the INFERCONSTRAINTS system variable.
Does Ctrl+Shift+I work in all AutoCAD versions?
The Ctrl+Shift+I shortcut toggles Infer Constraints in versions that include the Parametric feature (AutoCAD 2010 and later). If your edition or workspace does not include Parametric tools, the shortcut may have no effect.
How can I see which constraints AutoCAD has inferred?
Make sure CONSTRAINTDISPLAY is set to 1 to display constraint symbols. Use the Parametric tools to list or edit constraints on selected objects.
I pressed Ctrl+Shift+I but nothing changed. What should I check first?
First, type INFERCONSTRAINTS at the command line and check its value (1 = on, 0 = off). If it’s set correctly, verify CONSTRAINTDISPLAY and the Parametric tab toggle. Also ensure no other app is capturing the keyboard shortcut.
Can I permanently disable automatic inference and only apply constraints manually?
Yes — set INFERCONSTRAINTS to 0 or use the Parametric tab toggle to turn off inference. Then apply constraints manually from Parametric > Geometric when you need them.
How do I reassign or restore the Ctrl+Shift+I shortcut?
Open the CUI (Customize User Interface), navigate to keyboard shortcuts > Shortcut Keys, and add or modify the assignment for Ctrl+Shift+I to run the desired macro or command (or restore defaults by resetting your workspace/profile).
Will inferred constraints affect existing geometry if I enable it later?
When you enable Infer Constraints, AutoCAD may attempt to infer constraints for new operations and edits; it does not retroactively modify all existing geometry automatically in every case. To apply constraints to existing geometry, you can use manual constraint tools or specific infer commands if available.
Are inferred constraints included when exporting or sharing a drawing?
Yes — inferred geometric constraints become part of the drawing’s parametric definitions. When sharing, recipients will see and be subject to those constraints unless they disable constraint display or remove the constraints.