Three cards form a set if and only if: for every property, the three cards are either in total agreement or in total disagreement. In other words, three cards form a set when they satisfy these four conditions:
They all have the same shape, or they have three different shapes.
They all have the same number, or they have three different numbers.
They all have the same color, or they have three different colors.
They all have the same filling, or they have three different fillings.
Every card has four properties: