It's helpful to think of automotive platforms as parents, and to view the vehicles they spawn as children.

Not all children from the same parents turn out the same way. Some children succeed. Others fail, or don't do as well.

For example, there is Ford Motor Co.'s CD3 platform for mid-size cars and SUV/wagons. It is derived from the GGGY platform developed by Ford's Japanese partner, Mazda Motor Co.

In much the way that biological parents provide the basic genetic material for offspring, automotive platforms provide the underpinnings common to a number of vehicles. But, as is the case with children, commonality of effort -- good intentions, work, money and time invested -- does not ensure certainty of outcome.

Consider what happened here late last week.

Mazda introduced its newest sedan, the 2006 Mazdaspeed6, which goes on sale in the United States in November. "Mazdaspeed" is the name applied to high-performance versions of Mazda cars in much the manner that "AMG" designates the performance versions of Mercedes-Benz automobiles, or the "V" in the Cadillac CTS-V's name means that particular sedan is Cadillac's high-performance model.

Thus, the Mazdaspeed6 is the hot-to-trot iteration of the Mazda6 sedan. The Mazdaspeed6 exists because the Mazda6 has been a sales success in the United States. Both cars are based on Mazda's GGGY platform -- the same CD3 architecture that Ford uses for its new Ford Fusion, Lincoln Zephyr and the Mercury Milan reviewed in this week's On Wheels column.

The initial reaction from journalists examining the Mazdaspeed6 here was highly favorable. Most predicted that the car -- 5,000 copies of which Mazda plans to sell annually in the United States -- will be a winner. Handling, acceleration and styling got high marks. Most important, the Mazdaspeed6 won kudos for having a distinctive identity, albeit one enhanced by the addition of a 274-horsepower, turbocharged, 2.3-liter four-cylinder engine and some very smart suspension work.

No one expressed similar enthusiasm for the Mercury Milan, which was introduced earlier this year. No one hated the Milan. They simply were at a loss to say anything definitive about it. That is not a good thing, especially if consumers are equally befuddled.

"Well," said one Detroit journalist, "historically, Mercury has been offered as something between Ford and Lincoln in the Ford lineup."

"But what does that mean?" I asked. She hunched her shoulders. Everyone within earshot of our conversation shook heads and hunched shoulders, too.

Yet, no one had a problem putting a face, and a favorable one at that, on the Ford Fusion, or on the very definitely luxurious and appealing Lincoln Zephyr. All of those cars share the same CD3 platform, which can be used for front-wheel-drive or all-wheel-drive mid-size vehicles. But the Fusion and the Zephyr had identities. The Milan did not.

That is one of the pitfalls of platform engineering, a practice born of necessary cost efficiencies in the capital-intensive automobile manufacturing industry. Ford has not confirmed the figure, but industry reports say the company is investing only $1 billion in developing at least eight vehicles based on the CD3 platform.

Yes. That's "only" $1 billion. Without platform engineering, Ford would have had to spend $8 billion -- $1 billion each to develop eight different models using different platforms. That money does not include marketing and other costs.

Platform engineering saves big bucks, which is why all car companies use it in rolling out vehicles that often are visually different but technically and structurally the same beneath their sheet metal.

That being the case, it would seem that odds are in favor of platform-engineered vehicles sharing similar fates -- success or failure. But it just isn't so. Again, the family analogy is helpful. The most successful children tend to be those who accept and use familial nurturing without abandoning sense of self. They know who they are, even if their parents don't. They appreciate similarities with their siblings, but they don't succumb to them. Instead, even if they are viewed as being crazy, wild or otherwise unhinged, they strive mightily to make their own mark. In short, they'd rather fail at trying to be different than succeed at being like everyone else.

We notice those people. Whether we like them or not, we recognize who they are. We have feelings about them.

The same thing can be said of cars and platform engineering. Shared components and body structure are not the problem. The problem is forgetting or, worse, not knowing who or what you are. It's hard to appreciate an enigma, and harder still to try to sell one in a brutally competitive marketplace.

The Platforms

Ford's CD3 vehicles:

* 2006 Ford Fusion sedan

* 2006 Mercury Milan sedan

* 2006 Lincoln Zephyr sedan

* 2007 Ford Edge SUV/wagon

* 2007 Lincoln Aviator SUV/wagon

* 2008 Ford Freestyle wagon/SUV

* 2009 Ford Freestar minivan, which is moving from Ford's current "V" platform to a CD3 platform, and thus internally is regarded as Ford's "V2" project

* 2009 Mercury Monterey, another V2 project

Note: The planned 2007 Ford Fairlane crossover minivan has been switched from the Mazda-inspired CD3 platform to the Volvo-generated D3 platform, indicating that Ford may be ready to sell the Fairlane overseas, where the company believes the Volvo platform is preferred. Ford owns Volvo cars.

Mazda's GGGY platforms:

* Mazda6 sedan

* Mazda6 wagon, also sold as the Mazda Atenza in Japan

* Mazdaspeed6 high-performance sedan, which Mazda says is its "fastest-accelerating, best-handling and most advanced sports sedan"

* Planned Mazda CX7 crossover SUV/wagon

Mazda officials said at the Laguna Beach launch of the Mazdaspeed6 that they will introduce more GGGY-platform vehicles in the future.

The Mazdaspeed6 feels distinctive despite coming from a production platform that makes other models.