3 Opposition candidates. Under the first past the post FPTP voting system.
A vote for opposition is as good as voting for PAP.
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Criticisms of FPTP
Tactical voting
Main article: Comparison of instant runoff voting to other voting systems
To a greater extent than many other electoral methods, the first-past-the-post system encourages tactical voting. Voters have an incentive to vote for one of the two candidates they predict are most likely to win, even if they would prefer another of the candidates to win, because a vote for any other candidate will likely be "wasted" and have no impact on the final result.
The position is sometimes summed up, in an extreme form, as "All votes for anyone other than the second place are votes for the winner", because by voting for other candidates, they have denied those votes to the second place candidate who could have won had they received them.