What would you like.中的“would”为什么是过去式?

i would like an egg.中的would为什么用过去式? what would you like what would you like? What would you like _____noodles?What would you like _____pi what would you like,sir? What would you like-----it? What size would you like? What would you like to What would you like breakfast? what would you like best what drinks would you like? What would you like fordinner?