Relative adjectives express the properties of a substance determined by the direct relation of the substance to some other substance (wood – a wooden hut; mathematics – mathematical precision; history – a historical event; colour – coloured postcards; the Middle Ages – mediaeval rites).
The ability of an adjective to form degrees of comparison is usually taken as a formal sign of its qualitative character however, in actual speech the described principle of distinction is not at all strictly observed.
In order to overcome the of rigour in the definitions, an additional linguistic division based on the evaluative function of adjectives was introduced:
1) evaluative (giving some qualitative evaluation to the substance referent)
2) specificative (only pointing out the corresponding native property of the substance referent).