After ascertaining the total income from all sources, Law is either of the view that certain specified income might be exempted from taxation to encourage recipients or in fear of what recipients would do to the taxman.
In addition, between expenses carried in earning of that income, have to be deducted from the total income because the taxpayer may have incurred his own money already subjected to tax, which he may have expended in the earning of the total income. Furthermore, either tax already paid, as withholding or advance tax will need to be set off against any due tax.
Certain Relief Shelters are granted to certain specified people in certain specified conditions in order to reduce their tax liability to the extent of the relief. In this way, the government tries to mitigate the effect of tax on certain specified groups.