The graphical software Morph Moulder (MoMo) presented here was originally created for teaching the logical foundations of Head-Driven Phrase Structure Grammar (HPSG) in an e-Learning environment. It has then been extended to a treatment of description logics (DL), which are at present the standard formalism for building ontologies. With MoMo, students can construct interpretations of sets of formulae and check whether their interpretations model these formulae (called theory in HPSG and axioms in DL). MoMo also supports reasoning such as the construction of well-formed interpretations in the feature logic of HPSG and the automatic extraction of subsumption hierarchies in DL. It has been used successfully in several courses on HPSG linguistics, on computational grammar implementation and on the logical foundations of constraint-based grammar frameworks.