An evaluative concept entails that there is a value that has been placed upon an axiom, belief, or idea. This value can be either positive, or negative. The mere description of something is only one half of a complete evaluative concept; there also has to be an opinion about the value, or lack of value, of such concept for it to be considered evaluative.
Philosophy, or the love for knowledge, assumes that there is a constant pursuit of information through inquiry. This inquiry may either be scientific and exact, or sifted through deductive and inductive thinking. It is precisely that need for thought and analysis that makes it imperative to be "evaluative" when it comes to Philosophy. Hence, being "evaluative" is what lays at the core of the field; it is evaluation what brings Philosophy to life. Contrary to science, Philosophy is not exact, nor can it be proved correctly or incorrectly through a scientific method. As a result, Philosophy relies entirely on the evaluative concepts of which it is made.
Let us look at some examples that show how important it is to be evaluative for philosophical purposes.
A factually-descriptive concept would be: Agnosticism is a doctrine that affirms that there is no proof that shows that there is a God, or that there isn't one. This statement shows a fact: the actual description of Agnosticism. The statement does not give value to the premise as we are not "evaluating" the worthiness or lack of worthiness of Agnosticism.
Now, let's evaluate the concept of Agnosticism, that is, to make the concept "evaluative": Agnosticism is a (good/bad/correct/wrong/evil/rational) concept that assumes that there are no facts to prove the existence or lack of existence of God. Therefore, to be evaluative is to provide your judgement of the concept as you analyze/evaluate it.
In the field of Education there are two schools of thought that rule the pedagogical practice: the behavioral school of thought and the cognitive school of thought. Those who have analyzed (evaluated) the tenets of the behavioral school of thought would opt for teaching methods that involve conditioning and habit-formation. In contrast, those who go by the cognitive school of thought prefer to teach using developmental processes that occur naturally in the brain as a conduit for infusing knowledge.
Hence, Philosophy is created out of evaluative concepts and on the act of being evaluative. The only problem is to prove that the evaluation is actually fair. This is the difference between science and philosophy: one is exact, the other is highly bound to intellectual beliefs. Therefore, evaluative thinking continues to be at the heart of philosophical analysis.