If money income stays the same, but the price of one good goes up, the effective purchasing power falls, and vice versa.
Purchasing power is linked with Inflation.
... 2nd century - 3rd century - 4th century Decades: 190s 200s 210s 220s 230s - 240s - 250s 260s 270s 280s 290s Years: 237 238 239 240 241 - ...