They seem to be just perfectly ripe one day and then overripe the next. If they are picked sweet but still green, the ripening can be retarded for over one month. As long as they are kept cold they will ripen very slowly but pears will ripen rather quickly at room temperature. At home you can control the ripening by leaving most of the pears in the crisper of your refrigerator and bringing out just a few to ripen at room temperature. That way your will have just the number you need ready to eat at any one time and will not risk having the bottom of the bag becoming overripe before you can eat them.
Pears are ready to eat when they are yellow but still firm.
The texture of the skin also seems to change and become smoother to touch. The secret to keeping apples in prime condition is to handle them gently and to keep them cold. Apples bruise very easily, as do most fruit, and should not be squeezed or dropped even an inch. They should be refrigerated, preferably in the crisper so they will not dehydrate, unless you like apples softer than they are at the time you purchase them. If that is the case leave some at room temperature.