Opening One Spade
There are many advantages in always having a 5 card suit when you open 1 . When you open 1 partner is frequently forced to respond 1NT because partner does not have sufficient points to respond at the 2 level, and the weaker hand becomes declarer.
Let us consider hands when you only hold 4 cards in s and wish to open at the 1 level.
1. If you have a longer suit you will open that suit.
2. With balanced hands in your agreed no-trump range you can open 1NT.
3.With 4-4-4-1 hands (4 spades) the 'rules' are as follows: With a singleton open 1 (the middle suit of the 3 remaining). With a singleton or open 1 . Both these give you the best chance of finding a fit.
4. The only other hand type to consider is 4-3-3-3 , with 4 cards in s and more points than your no-trump range. In this case open 1 and re-bid 1NT etc over partner's response. Occasionally you will play at the 1 level with only 3 trumps. Acol bidders should be familiar with the 'prepared club' opening, its been around for years
What are the advantages of knowing partner has 5 cards in the opening spades suit?
1. With a singleton and 5 points you do not need to strain to bid 1NT 'to keep the bidding open'.Its unlikely you will miss game. Of course if you can bid 1NT, then the opner should always bid a second suit if she has one.
2.Should you need to give preference then a 5-2 fit usually plays better than a 4-3 fit, so knowing partner's spaders atre at least 5, enables you to make a better choice