When the opponents are playing a “Weak 1NT” opening bid (for example, 12-14 points), we need to bid only when we have a decently valued hand. We tend to bid with hands that would normally have overcalled at the 2-level, hands with about opening values. Here we are primarily bidding constructively because when the opponents open a “Weak 1NT” our side may still have game. If we bid destructively (with only shape and without much strength) then if partner has values, they may push the auction too high. It is common to use a different bidding system against the opponents’ Weak 1NT opening bid than the one you use against a strong 1NT opening. These systems usually contain a penalty double that allows us to show a very good hand as well, and thus penalize the opponents when partner also has some values.