I have moved into a house with an apple and a pear tree. Just after the flowers have fallen off the pear tree and the small pears appear, they turn black and drop off resulting in only one or two pears reaching maturity.
Good pears can be quite difficult to grow - more so than apples.
Their blossom opens early and is thus more frost-prone and there may not be enough pollinating insects around. But as fruit is setting on your tree, the culprit is almost certainly pear midge and if you cut a freshly dropped fruit open, you might find little whitish-orange maggots inside. These charming chappies move into the soil to pupate, then emerge as adults the following spring ready to lay their eggs. To succeed with pears, you need to break this cycle. Collecting up newly dropped fruitlets and disposing of them prevents the little devils from reaching the soil.