Abstract：By separating the activities of mind from the targets at which they are directed, some attitudes have been obtained. The attitudes are called 'mental modalities' which are described by mental modal words such as 'believe', 'like', and 'persist'. According to the types of targets, 'mental modalities' can be divided into three kinds: epistemic modality directed at the state of affairs, emotional modality directed at objects (including people), and volitional modality directed at actions. The three modalities can be regarded as 'de dicto', 'de re' and 'de acta' respectively. A mental modal proposition is formed when a mental modal word operates on its corresponding target. Mental logic researches the relationship between mental modal propositions formed by the same or different kinds of mental modal words. Unlike Piaget psychologic, mental logic is concerned with the structure of mind.
