Start with personal deductions that commonly affect net income on a Canadian return.
Personal deductions are amounts that can reduce income before taxable income is calculated.
Use this subsection when the question is about a claim that lowers income before tax is calculated, not a credit that reduces tax payable later in the return.
In practice, readers often move through this subsection in this order:
If you are really asking whether a claim reduces income or reduces tax payable, compare this subsection with Personal Credits.
If the question is really about work-related costs, move to Employment Expenses.