The regular, or normal, form of the past tense is made by adding the suffix -ed to the base form of the verb. There are many irregular verbs which form their past tenses in other ways. Some that give problems are in the category:irregular verbs. These are the patterns that non-native learners sometimes have to memorise in a more or less monotonous way - as do native speakers who have never thought much about writing grammatically. These are such words as 'swim' - 'swam' -'swum', 'think' - 'thought' and 'drink' - 'drank' - 'drunk'. In other cases, there are different spellings for the same forms, for example learned - learnt, leaned - leant, smelled - smelt and spelled - spelt. There are also cases where American and British English have different forms.
Prejudices also exist in favour of older past forms in certain verbs. The prejudices of academic teachers are not always fully supported by the evidence. The past form of 'to thrive' is throve, not
thrived, according to OED as well as the pedant who wrote this article. Most writers take the past tense of 'to strive' to be strove; strived is not used in modern English. The past tense of 'to wreak' is wreaked, though some academics say that it should be 'wrought' (they are wrong: 'wrought' is the (archaic) past participle of 'to work', a different verb altogether, with a not always dissimilar meaning).