There exist different types of gradual rules, involving graduality on the truth value, the possibility, the certainty associated with propositions, or dealing with the degree of similarity or the proximity of observations with reference propositions, or a graduality on the values taken by variables. In this paper, we describe the properties of gradual rules according to variations of values of the variables. Then, we extend the results to a graduality expressed through linguistic modifiers. Finally, we show that a gradual knowledge representation through modifiers can be linked with analogical reasoning.