world's entities into values and disvalues as seen by a social group, a culture, or a historical period. Axiological modalities are highly subjective categories: what is good for one person may be considered as bad by another one. Epistemic Epistemic modal operators (K-operators) reflect the level of knowledge, ignorance and belief in the possible world. Doxastic Doxastic modal operators express belief in statements. Boulomaic Boulomaic modal operators express desire. Modal logic Logic symbols Logical connectives