Strive

'To strive' is an irregular verb. Its forms are given here:

Base form	past tense	-ed participle	Remarks
strive	strove	striven	strived is also given as a regular variant of the past participle - although AWE would not recommend it for academic writing nor for the past tense.

This is one of the "the 250 or so irregular verbs" listed in Quirk 1985. The list "contains most of the irregular verbs in present-day English ... but is not meant to be exhaustive, particularly with regard to derivative verbs." AWE has copied most of the entries in that list. The verb 'to strive' belongs to Quirk's Class 4 C a.