Is it possible to get benefits of the two approaches (majoritarian and proportional) in a parliamentary system by making the lower house get elected by First-Past-The-Post and the upper one by party-list proportional? Like say: 600 representatives by FPTP and 90 senators by at-large PR? Could that mixture be the best compromise for all?

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    Are you asking in regards to any particular country? This would not make sense in the United States because the Senate is supposed to represent states instead of people. – Joe Aug 30 '19 at 22:46
  • "... in a parliamentary system..." – user26264 Aug 30 '19 at 22:48
  • Right, but benefits for who? is still relevant. The assumption that both houses exist to represent people is kind of present here. Plus some of the people on here who ask hypotheticals like this also like to do it because they want to make arguments compared to existing systems they find disappointing (e.g. mostly the US and UK at the moment) – Joe Aug 30 '19 at 22:53
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    So let me rearrange my question as a FPTP defender:is it possible to shut FPTP-haters mouths by introducing PR to the other house! LOL – user26264 Aug 30 '19 at 22:56
  • In effect, the upper house would represent party leaders, instead of specific geographic areas. – Jasper Aug 30 '19 at 23:16

Not only is it possible for nation states to use multiple voting systems in different legislative systems, but some are already doing it. As an example from the "A"s, Australia uses the Single Tranferable Vote (a proportional system, though not a single constituency list one) for its Senate, and instant-runoff (a single winner preferential system) for the lower House of Representatives.

Whether this system (or any other) is "best" is far more complicated, opinion-based and dependent on your prior prejudices. A usual argument in favour is combining the advantages of having a single geographical representative in the larger house with a breadth of views in the smaller. Counter-arguments include the greater difficulties and need for voter education with multiple systems and the complicated question of why one house is, or should be smaller than the other (this is much easier to defend in a federal system where one house is representing the interests of the provincial governments, rather than the people, than in unitary systems).