pronunciation - Is there a rule for the position of the accent (stressed sound) in words ending with -ative?

For example, can declarative be pronounced similar to declaration for the accent (stressed sound)? I thought before that sometimes the position of the "accent", or the stressed sound of a word, depends on how many syllables there are in the word.

But it seems that the words declaration and declarative have the same number of syllables, but declaration is stressed at the first syllable, while declarative is stressed at the second syllable. Is there a rule for this? Does the placement of the stress depend on the variety of English? (I suppose the word declarative is not pronounced with the first syllable stressed no matter it is British or US pronunciation?)