This paper aims at explaining the basic logical structure of the proportionality assessments, under the assumption that such assessments are based on quantitative reasoning, even when no numbers are explicitly given. First an analysis of practical rationality is proposed. Then the way in which norms have an impact on practical rationality is considered, distinguishing two kinds of norms: value-norms and action-norms. This analysis is then brought to bear on rights and their constitutional guarantees. It is argued that rights may be protected not only through action-norms, but also through value-norms. Finally some specific issues are considered such as how action-norms can be obtained on the basis of value assessments, and how proportionality assessment are constrained by the requirement of consistency with precedents.