Take this auction:
South
1 ♥
2 ♦
North
1 ♠
2 ♥
Is North’s 2 ♥ bid support (ie three cards — South has shown 5 ♥-4 ♦ ) or mere preference, perhaps on a doubleton?
The answer is preference. It would be nice for North to be showing three-card heart support but you simply cannot play the bid that way.

For what would you bid with these responding hands (after 1 ♥-1 ♠-2 ♦)?

♠ K982♥ J6♦ J2♣ Q5432
♠ J9842♥ 43♦ 432♣ AK5

2 ♥ is by far the best bid with both. Note that on the second, you actually prefer diamonds but the 2 ♥ 'false preference' gives opener another bid if he has a good hand. Further, a 5-2 fit is easier to handle as declarer than a 4-3 fit. Returning to opener’s first suit should always be treated as preference (although it may be support). The last two bids of these auctions, however, are support:

South
1 ♥
2 ♦
North
1 ♠
3 ♦

and;

South
1 ♥
2 ♦
North
1 ♠
3 ♥

You would not raise a second suit with fewer than four cards. Nor would you give jump preference with just a doubleton. The 3 ♦ bid in the first auction shows four(+) diamonds; the 3 ♥ bid in the second auction shows three hearts.

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