Anodes vs. Cathodes

[Jessica Nunez 1I]

When referring to the voltage of redox potential, how do we know which reaction is the anode and which reaction is the cathode?

[Niyanta Joshi 1F]

When the cell is spontaneous, the one with the highest reduction potential should be the reduction half-reaction and so it should act as the cathode. The one with the lower reduction potential as the oxidation-half reaction and so it should act as the anode.

[Ryan Neis 2L]

The reaction that is being reduced usually has the higher, more positive voltage, while the reaction that is being oxidized has the lower, more negative voltage

[Yutian Zhao -1J]

But how are we supposed to know whether the rxn is spontaneous or not?