Here’s an example from English. For most regular English verbs, forming the past tense is predictable, and is done by adding –ed to the end of the word: cook, cooked; walk, walked; step, stepped. Some verbs do not work this way. For example: eat, ate; go, went. These verbs are unpredictable in that you have to learn the past tense for each individually – they don’t follow any rule in the language. If you apply the regular, predictable rule of the English past tense to these irregular verbs (as children do when they are learning to talk), you would get: eated and goed. When conjugating any Tlingit verb, certain aspects of the verb are unpredictable in a similar way.