Given that the examinee knows the answer to item i if and only if he knows the answer to both item g and item h, a "conjunctive" item response model is found such that items g, h, and i all have the same mathematical form of response function. Since such items may occur in practice, it is desirable that item response models satisfy this condition. For models with two parameters per item, the most general functional form satisfying this condition is found. A third, "guessing" parameter may be added. The corresponding disjunctive model is also derived. (Author)