For the second year in a row, the issue of economic inequality was featured in President Barack Obama’s State of the Union Address. Even some Republican lawmakers have now dared to speak the “i-word.”

Though Obama predictably avoided comparisons between the earnings held by the top 1 percent and the 99 percent of Occupy Wall Street fame, the message was familiar: The widening income gap between the very rich and everyone else is a stain on the social compact and a serious problem for future economic growth.

Focusing on this income inequality is crucial. Lower incomes create an oxymoronic class of “working poor.” Inadequate pay hurts consumption and reduces tax revenues. People simply do more for themselves with more money, growing it into wealth for future generations — and as a cushion against economic downturns. A good job, as the president said, remains the best access to the promise of opportunity.

But there is another inequality that the president and others fail to address at the nation’s peril — structural inequality. This is the very foundation that reproduces widespread income gaps, the ground beneath the feet of income inequality.

It is not an abstract idea. We experience structural inequality — see it in the quality of local schools and their test scores, smell it in the access to healthy food or not, feel it in a sense of safety or danger as we walk the streets.