Taxable capacity or tax ability represents the extent to which an individual’s income and wealth can bear the burden of taxes. Financial thought has emphasized the necessity of establishing the principle of tax justice among taxpayers in a manner that considers taxable capacity, where taxes are imposed at varying rates that increase with the taxpayer’s income and decrease as it declines. The concept of taxable capacity necessitates the application of certain principles, such as the exemption of the minimum amount necessary for living, consideration of the taxpayer's family burdens, differentiation in tax treatment based on the source of income and the principle of progressive tax rates. Since taxes are among the most significant sources of state revenue, they are generally imposed on all taxpayers. However, the application of the principles of justice, in general and tax justice, in particular, requires taking into account all personal circumstances surrounding taxpayers. The state’s role is not limited to obliging individuals to pay taxes; rather, it must also consider their taxable capacity and family circumstances. Accordingly, most tax legislations have sought to provide a degree of personal exemptions, referred to as "allowances," which are legally exempt from taxation.