In the social sciences and philosophy, a positive or descriptive statement concerns what "is", "was", or "will be", and contains no indication of approval or disapproval (what should be). Positive statements are thus the opposite of normative statements. Positive statements are based on empirical evidence. For examples, "An increase in taxation will result in less consumption" and "A fall in supply of petrol will lead to an increase in its price". However, positive statements can be factually incorrect: "The moon is made of green cheese" is empirically false, but is still a positive statement, as it is a statement about what is, not what should be.
Positive statements and normative statements
Positive statements are distinct from normative statements. Positive statements are based on empirical evidence, can be tested, and involve no value judgements. Positive statements refer to what is and contain no indication of approval or disapproval. When values or opinions come into the analysis, then it is in the realm of normative economics. A normative statement expresses a judgment about whether a situation is desirable or undesirable, which can carry value judgements. These refer to what ought to be.
Use of positive statement
Positive statements are widely used to describe something measurable, like the rate of inflation in an economy. They are mainly used in explanations of theories and concepts. Using a positive statement does not mean you can't have your own opinions on issues. However, when you are writing academic essays it's important to use positive statements to support an argument, since it can be verified by evidence.