The priorities you place on these functions can influence what car you buy. But sometimes a car chosen for Function A, say, may have surprising claims on Function B. And Function C can lead to all sorts of trouble.
So it is with Citroen's new Xsara Estate. In Function A terms its purpose is clear. Forget the lifestyle estate idea, Audi A4 Avants, BMW Tourings, Volvo V-whatevers; this is a smaller, cheaper car in which load-lugging is central to its being. But it's a Xsara, and Xsaras, despite a visual personality bordering on the anodyne, are entertaining to drive, with perky engines and responsive handling. So that's Function B, coming up hard now into contention.
And C? As I said, it's a Xsara, from today's super-sensible Citroen company, all sales-focused and customer-responsive. Buy a Xsara Estate, and clearly you are Mr/Ms Sensible. So why was it, then, that at the UK press presentation of this useful but heartrate-neutral car, the Citroen people suddenly linked the new Xsara Estate to the great tradition of the DS Safari and - sacre bleu! - the Traction Avant Commerciale? This latter, by the way, was an opening-rear relative of the car made famous by Inspector Maigret.
The past has been taboo for a while at Citroen, but a thaw is starting. Or maybe there's a more pragmatic explanation. The Xsara range has not captured the buying public's imagination (and its money) as its makers hoped it would, mainly because of a shortage of Function C - credibility. Link the Xsara Estate with cars perceived as interesting and glamorous, goes the thinking, and maybe the new car will soak up some Function C kudos where all else has so far failed (Claudia Schiffer's dishabille in the Xsara Coupe ad notwithstanding).
It helps that the Estate is aesthetically the happiest Xsara; it's more resolved around the rear end, thanks to a gracefully rising waistline that reaches a proper conclusion instead of being chopped prematurely. And, yes, it's a good car. It swallows more stuff than immediate rivals, slim roof pillars make it much lighter and airier than other Xsaras, and the estate-car side of things is intelligently conceived.
There's other cleverness, too. Eschewing the trend towards body-colour- painted bumpers that are expensive to refurbish post-bump, Citroen fits the Xsara Estate with black plastic bash-surfaces in sections. Scrape a corner, and the corner is all you replace. And the top Exclusive version has an automatic windscreen wiper setting that works out when to switch the wipers on or off. Believe it or not, it works.
You get a choice of 1.4, 1.6 and 1.8-litre petrol engines, the middle one of which strikes a particularly good compromise between pace, price and smoothness, and two 1.9-litre diesels, with or without turbo. The interior is solidly constructed, the seats are comfortable, life is sweet. Apart from one surprising flaw.
Larger Citroens are noted for the smoothness of their ride, because their hydropneumatic suspension compensates for the weight. But the Xsara, like the ZX Estate before it, has simple steel springs, rather stiff, to cope with heavy weights, and therefore unyielding. With just two people on board, the Xsara Estate proved the most agitated Citroen, apart from sporty derivatives, that I have ever experienced. By my judgement, it matters. But by the stark logic of Function A, unless your life revolves around eggs or fine-cut crystal, it almost certainly does not.
Price: pounds 13,610 (1.6 LX) Engine: 1,587 cc, four cylinders, 90bhp at 5,600rpm. Transmission: five-speed gearbox, front-wheel drive. Performance: 112mph, 0-60 in 11.6sec, 31-36mpg.
Daewoo Nubira 1.6 SE Estate: pounds 12,995. Well-made, comfortable but characterless load-lugger from Korea. Worth a look.
Ford Escort 1.6 LX Estate: pounds 13,720. Capable but dated, archetypal TV rental company transport. To be replaced in the autumn.
Peugeot 306 1.6 LX Estate: pounds 14,195. The march of the 1.6 LXs continues. Less space, more panache than Xsara.
Vauxhall Astra 1.6 LS Estate: pounds 13,545. New Astra is delightful to drive, but cabin is deeply dull.