What is the Difference between positive and normative science?

A Normative Theory expresses a judgment about whether a situation is desirable or undesirable, and is based upon some moray or standard. The world would be a better place if the moon were made of green cheese, is a normative statement because it expresses a judgment about what ought to be. Notice that there is no way of disproving this statement. If you disagree with it, you have no sure way of convincing anyone, who believes the statement, that it is incorrect.

A Positive Theory expresses an opinion on a condition, assuming what is, and that contains no indication of approval or disapproval and is not based on any standard. Notice that a positive statement can be incorrect. The moon is made of green cheese, is incorrect, but it is a positive statement because it is a statement about what exists.