What does *losing its purchase on reality* mean in the following sentence?

Question

What does "losing its purchase on reality" mean in the following passage (emphasis added)?

Vanquishing poverty gave the Bank a new focus and a credible mission, and it added moral underpinnings to the economic case for resource transfers from the rich to the developing nations. Moreover, growth economics, which was in danger of losing its purchase on reality, acquired a tangible purpose. With faster growth, a nation's domestic product would increase, and the incomes of the poor would be more likely to rise.

^{Development Economics through the Decades: A Critical Look at 30 Years of the World Development Report, Shahid Yusuf, page 21}

Answer 1

I suspect that the word that is causing you trouble is "purchase". "Purchase" here does not mean "the act of buying", but rather definition 2, "a hold or position". That is, you can say, "As he climbed the mountain, he found a purchase for his foot in a small crevice", or "I got a firm purchase against the wall to help me push the heavy piece of furniture." (Probably doubly tricky here because the fact that we're discussing economics likely makes you think of "purchase" in the sense of buying.)

"Purchase on reality" is a somewhat common phrase meaning a hold on real life, that is, an understanding of what is actually happening around you, as opposed to a delusion. We say that someone going insane has "lost his purchase on reality", like a mountain climber could lose his footing and be in danger of falling off the cliff. The phrase is often used in the negative this was "lost his purchase on reality", "has no purchase on reality", etc, to describe some person or school of thought that we believe is not practical or realistic.

So here, the writer is saying that "growth economics" was becoming unrealistic or impractical, but now something has happened to give it a practical purpose. (I presume that what that "something" is is described in context.)

Answer 2

purchase

can have the meaning of "leverage" or "grip" when referring to heavy items either literally or metaphorically, you phrase means

losing its grip on reality

Answer 3

"Purchase" can be used not just as a synonym for "grip", but also for mechanical advantage.

If you have a pulley that allows you to move a heavy object 1 foot for every 2 feet of rope pulled, the "purchase" is often referred to as 2:1. So a strong "purchase" might mean you really have strong physical leverage over something ... in this case reality itself.