What’s a Threat?

     I was browsing Purdy’s The Search for Chess Perfection the other day and there was a chapter on How to Think in Chess where he addressed threats. Purdy stated, “Threats are the basis of winning chess.” OK, so exactly what is a threat?
     Purdy points out that vague statements like, “He threatens to trap my Queen.” lies at the root of many bad moves and thinking of threats in words will often lead you astray. When dealing with threats you must look at the actual move that you think is a threat and then by calculation determine if the threat is real or not.  Purdy adds that if you sit in on a post mortem with strong players and they are examining a threat, they get down to business and look at moves, not words.
     I would add here that the same holds true when you are considering a 'threatening' move.  I have in mind some internet games where my opponents have played moves like Bxh7+ apparently with the assumption they are threatening a winning mating attack.  Unless you have a Grandmaster's intuition, some attempt, however feeble, should be made at calculating the results. I have in mind positions like this:

White to play

     My opponent played 9.Rxh5?! which is not all that great even if he follows up 9...gxh5 with 10.Ng5 and probably 11.Qh5.  Instead, after 9.Rxh5 gxh5, he followed up with yet another sacrifice, 10.Bxh7+??, and had no attack.  For me it was simply a matter of playing carefully so as not to make any stupid mistakes and trade pieces at every opportunity.  The guy resigned late at move 31.
     Purdy defines a threat as a move your opponent could make if it were his turn to move that would be damaging to your game. Likewise, a threat is a move you could make if it were your turn to move that would be damaging to your opponent’s game.
     He advises that when it is your turn to move and you are not sure if your opponent’s threat is real, the best thing to do is imagine that he could not execute the threat. What would your best move be? Visualize the position after you make your move then see if his threat would really work. This is also a good idea even if you know his threat is real. Why? Because if you know the threat is real, you will usually start playing defensively and as a result, you will often miss a lot of opportunities for counterattack. Here is a simple example he gave to illustrate the point:

     This is a position from Capablanca – Tartakower, Carlsbad 1929. Black has just played 8…Nc5 threatening to capture the e-Pawn. Capablanca wants to develop his N to c3 which also defends the e-Pawn so he played 9.Nbc3. Makes sense, right? 
     No, because Capa was thinking in words, not moves. Let’s put Purdy’s advice into practice: imagine that it is black’s move and he plays 9…Ncxe4. Now 10.f3 and the N simply goes back to c5. But what if c5 was guarded?
    9.b4! and now black can’t capture the e-Pawn because after 10.f3 the N doesn’t have any escape squares. The “threat” to capture the e-Pawn is not a real one and after 9.b4 black has to retreat and has lost time. In addition white has gained space on the Q-side.