Industrial Engineer · phase 3 of 16 · noun

Permissive

Condition that must be satisfied before an operation is allowed to start or continue.

The Explain card

Plain English: A permissive is a condition that must be true before an action is allowed to begin. It is checked at the start, and once the action is running it may or may not keep watching.
Example: The pump start needs suction pressure above the minimum and the discharge valve open. Both are permissives, and the start button does nothing until both are satisfied.
Why it matters: Permissives are the difference between a machine that starts safely and one that starts and then destroys itself. Listing them on the HMI as a ready checklist turns a mysterious refusal to start into a line that says which one is missing.
Hook: Everything that has to be true before you are allowed to push the button.

How the word is built, where it came from, and what it sits beside in memory.

In a sentence

The PLC verifies the cooling-water permissive before energizing the variable frequency drive output contactor.

How it is built

Where it came from

Origin: Late Latin permissivus, from Latin permittere, meaning to let pass or grant
Entered the language: 15th century
What changed: It began as an adjective associated with granting leave, then became a noun in control engineering for a qualifying logic condition or signal.

How it is spelled

Pattern: The suffix -ive forms permissive from the Latin-derived stem permiss-.
Pattern: The double s is retained before -ive, as in permission and permissible.
Breaks the pattern: The related verb permit has one s and changes the stem ending from -mit to -miss in permissive.

Spelled like

Broken into chunks

What it sits beside

Same subject

Same shape

control logic qualifiers

motor-start inputs

Phase 3: PLC Program Organization and Execution

How the logic is arranged and how the scan actually runs it, which is the difference between code that works and code that works every time.