【Certain】 , 【inevitable】 , 【necessary】 are comparable when they mean bound to follow in obedience to the laws of nature or of thought.
What is 【certain】 does not admit of being described as probable even in the highest conceivable degree and is beyond question or dispute.
What is 【inevitable】 (see also 【INEVITABLE】 ) is as it must be (sometimes should be) according to some unchangeable law (as of nature, of logic, or of beauty). 【Inevitable】 often carries little suggestion of unavoidability but stresses finality (as in truth or rightness) or an ultimate character (as perfection).
What is 【necessary】 is logically or naturally 【inevitable】 and cannot be denied without resulting contradiction or frustration.