what is the difference between definite and definitive?? what both of them is the best used in this sentences : definite means conclusively and without doubt == as in a yes or no answer. definitive means something has encompasses information that is conclusive and has an aspect of proof about it. As in - The pathology reports were defnitive, the patient had the disease. - The results are not definite/definitive???? <-- you could say both of these - at a definite/definitive time???? <<--- only a definite time - definite/definitive proof???? <<------- both of these are possible. and what is the difference between for and towards?? - I am not sure what you mean here. what is the best sentences? "He is an expert by definition" or " He is by definition an expert" ?? You could say either sentence. Whether they are unusual depends on context.

definite / definitive. The first just means 'certain'. the second has some other meanings. You can apply it as an adjective to something, that gives the thing a quality of 'defining' the class of thing. E.g. He delivered the definitive lecture on the subject' For / toward: The first means something has been assigned for a purpose. This is a jacket for your brother. The second implies a direction of movement or purpose. 'He threw the jacket towards his brother'. Or 'He gave some money towards your education'. An expert by definition - there is a double meaning here. You are saying, that he is so expert that one could use his example to define the meaning of 'expert'. The second meaning then, is saying that as the term 'expert' has been defined, he clearly and measurably matches the definition. It means both things at the same time. It is really a superlative.