Americans will be seeking out smaller houses on smaller lots and will be driving smaller cars.

Definitions shift. At the start of the 20th century, immigrants saw a home as an anchor in a safe harbor. Whether a ramshackle cottage, a tenement, or a farmstead amid a wasteland, the definition of home connoted a state of mind and not just the state of the physical structure.

Poor- to middle-class Americans rarely owned, much less hoped to own, those homes. They could not afford them — banks wrote five-year loans and demanded 50 percent down payments. The wealthy owned mansions, but a peripatetic class that summered in Newport, Rhode Island, wintered in Manhattan, and toured Europe in between did not want anchors. Ironically, while replete with a number of houses, the privileged of that era were "home-less."

Fast forward to the New Deal and post-World War II. Government subsidiaries, in the form of the federal housing and veterans administrations, ushered in the 20-year, fixed-rate mortgage with a 20 percent down payment. A new American middle class — homeowners — was formed. The American dream (think Levittown) was a three-bedroom expandable Cape Cod — and the factory worker could own one.

A home became a vehicle for enforced savings, a hedge against inflation. The family that bought a three-bedroom Cape in the 1960s expected to pay off the mortgage, celebrating with mortgage-burning parties, and to have a post-retirement nest egg, the remainder of which they could bequeath to their children. The home still remained primarily an anchor. With a new job, or a new baby, a family might pull up stakes, but most stayed on, and instead, might expand their house by building an extension.

The 1990s ushered in a flurry of economic phenomena: new mortgage products (interest only, negative amortization, no downpayment), the bundling and selling of mortgages to the secondary market, the ascendance of mortgage banks and mortgage brokers, and the demographic surge of new households in various parts of the country. Everybody, even those with shaky credit, could buy a home. In addition, the value of every home seemed to outstrip inflation.

The definition of a home changed: It was now an almost fungible investment. Owners used their homes as ATMs (automatic teller machines), borrowing against their ever-rising equity. "Flipper" entered the lexicon, applying to buyers who expected to sell their new home within a few years — at a profit — and then repeat the process.

Seeking more investment value, buyers sought bigger houses — the average square footage of new homes went from 1,500 square feet in 1970 to 2,300 square feet in 2000 — with more fireplaces and more bathrooms. Lots grew larger when buyers began to move to the exurbs. The year 2008 brought new economic phenomena: rising utility costs, gasoline prices, unemployment — and plummeting house prices.

Losing its investment strength, the home once again connotes an anchor — a place where people feel safe, connect with neighbors, raise children — in short, where they simply live.

While owning a home can be a hedge against inflation, the new/old definition of home-as-anchor includes renting a home: One-third of the country rents. In spite of public policies designed to help everyone become a homeowner, there is no reason for every renter to buy a house. Actually, under some boom-times mortgages (with no downpayment and no principal reduction), owners were, in effect, "renting" their homes.

Home-as-anchor forces a reconsideration of both size and location. Soaring energy prices make bigness a liability — and green features (like clotheslines, porous paving and high-efficiency water heaters) an asset. Similarly, rising gas prices will encourage buyers to reconsider urban living.

So, it is "back to the future." In the not-so-long-ago time of easy mortgages and careening prices, homes were assets to be bought and sold. As the mindset of home-as-anchor takes hold once again, families may recognize that a home is not a fungible asset, but a stake in a community — one that can be rented or owned.

Nicolas P. Retsinas is director of the Joint Center of Housing Studies at Harvard University. He wrote this commentary for The Advertiser.