. . . Let us think about Madame Règle. She has the potential to have lunch at Latimer Sauf’s restaurant every day. He always has a table for his friends and she has enough money. However, her work with Paris haute couture designers often keeps her over the lunchtime. Her coming to lunch is probable, but not certain. CERTAINTY requires both potentiality and probability. Let us think about Monsieur Sauf’s birthday. Madame Règle will come to meet him. It is certain.