In a first past the post system, voters vote for their favorite candidate and the candidate which gathers the most votes in the constituency wins the election. The merits of FPTP system are-
1. It is simple to understand. In countries like India with such low literacy rate, the alternative voting system like Party-list PR will be very complicated to understand.
2. It is cheaper and quicker to administer. FPTP is way cheaper than another kind of voting systems. It is fairly quick to count the votes and work out who has won.
3. Since the party with the majority forms the government. Single party governments by and large don't have to rely on support from other parties in order to pass legislation.
The Demerits are-
1. Representatives can get elected with small amounts of public support, the size or percentage of voters or winning margin is irrelevant what is important is that the candidate must have got more vote than the other candidate.
2. It restricts the voter's choice as parties are not homogenous and do not have a unified voice. There are many viewpoints amongst a party and if the part preferred candidate in a constituency has views with which a voter doesn't agree to, the voter cannot express this at the ballot box.
3. FPTP restricts the choice of candidate as the party will offer the safest looking candidate the chance to stand for election rather than equal representation from minority section and women.