Why are there four combinations فَعَلَ، فُعِلَ، مَا فَعَلَ and مَا فُعِلَ?

Complete Past-Tense Paradigm: Active, Passive, Affirmative and Negative

• There are four tenses
• Active/passive and affirmative/negative are independent distinctions
• There are four masculine persons
• Every past verb has four root letters