OTTAWA -- The Supreme Court of Canada issued a landmark ruling on Friday in rejecting the appointment of Justice Marc Nadon to the high court. Here are five key points to consider:

1. It was the second Supreme Court rebuke for the Harper government this week. On Thursday, the court ruled that a government attempt to take away early parole rights from some prison inmates was unconstitutional. The justices appear to be sending the message that even a majority government can't have everything its own way.

2. The justices placed constitutional armour on the Supreme Court Act, saying the federal government cannot, on its own, change the criteria for selecting high court judges. Changes to essential features of the court would require the consent of at least seven provinces representing at least half of the population.

3. In an unusual move, the six members of the majority demonstrated a united front of sorts by all taking shared credit for writing the decision. Normally, one or two judges write the decision with the others simply concurring.

4. The ruling clearly caught the government off-guard. The Prime Minister's Office said in a statement that it was "genuinely surprised" and that it would take the time to consider its options.

5. Prime Minister Stephen Harper appointed five of the eight sitting justices, but that doesn't give him leverage on the bench. The justices rule as they see fit and that may be of concern to Harper, who is looking to the court for guidance on how far he can go on Senate reform without starting a constitutional fracas.