| 21. | In any case, different answers to such questions yield different systems of modal logic.
|
| 22. | He wrote important papers on free logic, general modal logic, and natural deduction systems.
|
| 23. | S4 and S5 are the beginning of what is now called normal modal logic.
|
| 24. | Pratt was an Assistant Professor at dynamic logic, a modal logic of structured behavior.
|
| 25. | Semantic approaches dealing with modality are traditionally based on the principles of modal logic.
|
| 26. | Epistemic logic is a modal logic dealing with the notions of knowledge and belief.
|
| 27. | In a classical modal logic, each can be expressed by the other with negation:
|
| 28. | The expansion rules depend on the particular modal logic used.
|
| 29. | However, relatively few systems of modal logic can be formalised directly in natural deduction.
|
| 30. | These methods have also been extended to modal logic.
|
