Choose the antonym of "restricted"

Concept: An antonym is not simply a word that feels opposite in tone; it is the word that sits at the opposite end of the SAME semantic dimension as the target word. The method is therefore two steps: first name the dimension the target word measures, then take the option that occupies the far end of that same dimension. An option that measures a different dimension, or that sits at the same end of the right dimension, is not an antonym however familiar it looks beside the target.

Application: restricted is the past participle of restrict (Latin restringere, "to bind back"), and it means kept within limits — access, movement or quantity has been fenced in. The dimension it measures is thus how freely something may be entered, used or extended. Step two asks for the word at the far end of that same dimension: the word meaning that no such fence is in place, so that entry or use is freely available. That word is open. An open competition, open access or an open border is exactly one on which no such limit has been placed, so open is the antonym of restricted.

Cross-check — run the same two-step test on the remaining options:

• limited measures the right dimension (extent, amount, scope) but sits at the same end of it as restricted: both say that a boundary is in place. Same end of the same dimension makes it a synonym, not an opposite.

• selective measures how narrow the criteria for choosing are. Choosing by criteria narrows what gets through rather than removing the fence, so it lies on the same side of the access dimension, not at its far end.

• cautious measures how much care is taken before acting — a dimension of behaviour and attitude, not of access. A word on a different dimension cannot be the opposite end of this one, whatever its tone.

Result: the antonym of restricted is open. Standard dictionary thesauri bear the same split out — they list open and unrestricted among the antonyms of restricted, and limited among its synonyms.