There is no such thing as arithmetical ability—only arithmetical abilities

Thus far, we have been discussing arithmetical ability as though such a thing existed as a single entity. However, there is extensive and increasing evidence that there is no such thing as arithmetical ability: only arithmetical abilities. Although some people tend to do well on most numerical tasks and some people to do badly on most numerical tasks, it is quite possible for the same person to find some numerical activities easy and some difficult.