Abstract:  It has been found that children appreciate the limited substitutability of co-referential terms in opaque contexts a year or two after they pass false belief tasks (e.g. Apperly and Robinson, 1998, 2001, 2003). This paper aims to explain this delay. Three- to six-year-old children were tested with stories where a protagonist was either only partially informed or had a false belief about a particular object. Only a few children had problems predicting the protagonist’s action based on his partial knowledge, when he was only partially informed about a property of the desired object (e.g. he knew that it was a Lego® block, but not that it was a red Lego® block). But many had problems making the correct action prediction when he was only partially informed about dual identities (e.g. he knew it was a dog, but not that it was also an eraser). About as many children made an incorrect action prediction for partial knowledge problems involving dual identity as answered higher-order belief questions incorrectly. In contrast many more children answered first-order false belief questions correctly, as many as correct action predictions when the protagonist was partially informed about a property of an object. The results support the claim that children have a specific problem with dual identity, rather than a broader problem representing partial knowledge.