U.S. personal income jumped in July, but consumption didn’t. That has economists praying for consumers to start spending their tax rebate cheques as soon as they arrive.

“Our off-the-cuff, seat-of-the-pants, back-of-the-envelope model of U.S. consumers is that money comes in the door and is applied to the credit card bill in full. Then, if there’s any spending limit still available on the card, new spending is soon forthcoming,” says BMO Nesbitt Burns. “Clearly, the first wave of July tax rebate checks, which boosted disposable income 1.8% in real terms, arrived too late to go through the card payment process and didn’t immediately spur spending.”

Economists are hoping against hope that something spurs spending, with the consumer the last line of defense between slow growth and outright recession. “The economy needs every smidgen of spending that can be squeezed out of households since most other demand-side categories are in decline at this point,” says BMO.

This higher spending wasn’t in evidence in July, and BMO says there’s little evidence of it in August so far. “But don’t bet against the consumer yet — hopefully, outlays will be heading up by September. The trend is roughly on track for growth in consumer spending near 2.5% in the third quarter.”

The markets and the Fed will regard this report as neutral, says BMO, but it says the economy needs more than sitting in neutral. “We need to see evidence that the rebate program is working. If not, batten down the hatches,” it warns.