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.