According to Adam Smith, there are four canons or maxims of taxation. 

They are as follows: Canons of Taxation:

1. Economical 

2. Equitable

3. Convenient 

4. Certain 

5. (Efficient and Flexible)

1. Canon of Ability: 

1. The Government should impose tax in such a way that the people have to pay taxes according to their ability. 

2. In such case a rich person should pay more tax compared to a middle class person or a poor person.

2. Canon of Certainty: 

1. The Government must ensure that there is no uncertainty regarding the rate of tax or the time of payment. 

2. If the Government collects taxes arbitrarily, then these will adversely affect the efficiency of the people and their working ability too.

3. Canon of Convenience: 

1. The method of tax collection and the timing of the tax payment should suit the convenience of the people. 

2. The Government should make convenient arrangement for all the tax payers to pay the taxes without difficulty.

4. Canon of Economy:

1. The Government has to spend money for collecting taxes, 

for example, salaries are given to the persons who are responsible for collecting taxes. 

2. The taxes, where collection costs are more are considered as bad taxes. 

3. Hence, according to Smith, the Government should impose only those taxes whose collection costs are very less and cheap.