Pears which are half the size of a typical "grocery store" pear are undoubtedly edible. "Ornamental" pears, like "Bradford" are a different species which bear round, brown, pea-sized berries which ripen in autumn, and which are pretty much inedible even to birds, from what I've observed in my neighborhood.

However, anything which looks like a traditional pear, even if quite small, is a pear, and should be very edible. Please don't be biased by the size, remember, pears grown for "grocery store" sales are usually the largest and choicest fruits, because stocking oversized produce encourages consumers to buy more poundage, thereby spending more money.

Some pear varieties, like Seckle, are only two to three inches long naturally. Others, like the traditional Bartlett, Bosc, Anjou, and Comice, will bear much smaller fruit than seen in the grocery store, unless the fruit is thinned, the tree is pruned properly, fertilized, and sprayed regularly like a commercial grower would do. Untended fruits may be smaller, but there are usually more of them.

Taste. Pick. Enjoy.