I came across a post on reddit/r/allthingsterran regarding how to react to command centre first. Despite it is a frequently asked question, the answers provided by the community are only limited to how to be aggressive. This post looks at the same issue from a different angle.
Background
The common answers suggested by the community almost always revolve around one key approach: be aggressive. For example, “when you see command centre first, you should make Marines, Tanks and Banshee to punish the opponent for being greedy”.
To begin with (look at the link I shared earlier), the title itself, “Best way to punish CC first TvT”, indicates that the player has already dropped into the loophole of functional fixedness. The player is only looking for an answer that can “punish” the opponent, and it typically shapes up to some sort of aggressive options. If you read through the comments, the community is suggesting various ways on how to be aggressive.
Indeed, it seems intuitive to react aggressively to an economical build based on the rock-paper-scissor analogy: Aggressive > Economical > Defensive > Aggressive
However, will you go for an economical build if opponent can react from a “normal” build and kill you? The answer is no. Thus, from the perspective of the player who chose to use an economical opening, s/he has plans to hold off your reactive aggression. For example, TaeJa’s command centre first ensures that the bases are well defended against Banshee at the standard timings. When your aggression has been held, you are way behind in every manner. It is perhaps more risky to react aggressively than to open up economically. Of course, if you open up with 2 rax or 8/8/8 Reaper, you are likely to punish 14CC hard. But that is not a reaction anyway.
Proposed solution
Back to the question, how do you react then?
You can simply be even more economical. For example, you use a 15 gas build. Instead of getting Marines and Hellions, which is what the build order does, you can simply cut unit production (not Scv) and get a third command centre. Polt did just that against TaeJa in WCS Season 2.
Polt scouted TaeJa’s opening, he sticked to his general build order and got a factory and a starport. But he did not produce any unit from the barracks, factory and starport (except the first two Marines) until he got his third command centre up. TaeJa was not going to attack anytime soon because he went for a 14CC. So Polt could cut corners and stop unit production for the 400 mineral.
15 gas can be considered relatively economical on an “economical scale” compared to 12 gas or 13 gas builds, because 15 gas gets an early command centre anyway. You can do the same for other aggressive openings like 12 or 13 gas simply by altering your build order slightly. It is not wise to cut unit production and go straight into three command centre because you will bank up much gas unless you pull Scvs out of refinery. Thus, you can stick to your plan to get cloaked Banshee and get three command centre behind it. Just produce two or three Banshees, and nothing from the barracks and factory. Then, use the mineral on command centre. You don’t need Viking or Raven just yet because opponent does not have the tech for Banshee or Medivac. Of course, if you scouted that opponent is going for Banshee with your own Banshee, get Viking and Raven accordingly.
This can be applied to other match up. For instance, you scouted a nexus first opening. Sure, you can try to build two more barracks and be aggressive and pray that you can overcome the Mothership Core. You can also react by being even more economical than your opponent. Let say you go for a one barracks expand. You can react by doing a one barracks expand into another command centre (3x command centre).
The rationale behind the economical reaction is the relativity in rock-paper-scissor analogy: Aggressive > Economical > Defensive > Aggressive. By going for an economical opening, opponent has to defend in order to leverage from the investment in economy. You can shift his “economical” status to “defensive” by being even more economical than him. Thus, instead of playing an aggressive > economical game, you simply shift it into an economical > defensive game.
Summary
Being aggressive is not the only reaction to an economical build. You can react by being even more economical. Instead of playing an aggressive > economical game, you can shift it into an economical > defensive game.
TerranCraft 
It is logic. But as a mid master player, I tend to have more troubles with my build if I change it so much (going 3CC instead of innovation 15gaz expo). It is very difficult to have loads of timings in mind while changing your build slightly when you haven’t practiced it before :/ (you then don’t get your barracks at the correct time, upgrades are too early or too late, …)
I can totally understand what you mean. I had floated 1500 mineral in mid game because I didn’t adapt to it well enough when I first did this.
I wonder how progammers do to be able to change their build so well while being able to multitask without making any mistake. Do they train every adaptation of their build (as if they imagine their opponent does a CC first) or are they just so good (and they play so much) that they can change their build at any time they want into something very different..
I’m not sure about them. But the way I do it is that I don’t remember build by heart (unless I am learning a completely new one). I know the convergent points and I try to meet them although the build order has been shuffled. It is really about knowing the convergent point. Altering things according to situation makes the game fun. Think of it from Zerg’s perspective, they are also doing more or less the same thing, do they follow build order to drone or get units? There is a rough “guide”, but they still have to adapt accordingly.
Great article as usual. When you wrote “By going for an economical opening, opponent has to defend in order to leverage from the investment in economy.” I don’t quite follow. Do you mean “By going for an economical opening, opponent has to defend because he assumes you are going to attack” ?
I mean opponent is going for an economical opeing (CC first for e.g.), and s/he to defend against any form of attacks. In general, you cannot be aggressive and be economical in an opening. May be I didn’t phrase it well enough. =/