‘When John and Mary went to the shop, John gave a drink to ___.’ You say Mary — and so does a language model, through a precise little circuit. An S-inhibition head spots that John is the REPEATED subject and SUPPRESSES it, so the name-copying head is left pointing at the other name. Slide the sentence and watch the veto land.
This is the IOI (indirect-object identification) circuit (Wang et al. 2022). Two names appear; one is repeated as the sentence’s subject. An S-inhibition head detects the DUPLICATED name and writes a signal that suppresses the name-mover head’s attention to it — so the name-mover copies the OTHER (indirect-object) name into the prediction. The instrument runs the template. A fail-loud self-check throws unless it identifies the repeated subject and returns the non-repeated name as the answer, for each sentence.
A rule-level demonstration of the circuit’s LOGIC across a handful of names; the real circuit is a distributed set of heads (duplicate-token → S-inhibition → name-mover) found by causal patching, is graded, and can fail on harder sentences. The identify-and-suppress logic shown is exact.