When faced with pears
firm as crabapples
that could dent someone’s skull if launched correctly, you'll most likely put them in a paper bag and let them sit on the counter for a day or two. Why? 'Cause that's what your momma
taught you to do.
Apples, pears, peaches, plums, nectarines, and some other fruits produce ethylene, a natural ripening hormone. A paper bag will keep the gasses close to the fruit, which stimulates the ripening process. A paper bag is ideal as it still allows moisture in and out. If you were to attempt this with a plastic bag you might find a fuzzy mess where your Bartlett pears once were.
You can also take fruit that does not produce, or produces little, ethylene—such as kiwi or bananas—and place it in a paper bag with an apple and it will ripen quicker than it would have on its own. Ethylene can also 'save' stale bread: place the bread in a paper bag with an apple or two and it will regain its softness and flavor.