Many people, not to say all, call "theory" the huge number of openings and their variants.

I do NOT call that a theory, it's just a great database of lines.

Would a database of thousands of English sentences be called a grammar ? No.

From Wiki: The Greek theoria (θεωρία), from which the English word "theory" (and theatre) is derived, meant "contemplation, speculation, a looking at, things looked at", from theorein (θεωρεῖν) "to consider, speculate, look at", from theoros (θεωρός) "spectator", from thea (θέα) "a view" + horan (ὁρᾶν) "to see". It expressed the state of being a spectator. Both Greek θεωρία and Latin contemplatioprimarily meant looking at things, whether with the eyes or with the mind.

Elementary, my dear aln67.  QED !

One of the most annoying things ever.  "Evolution is just a theory."   PUKE!!!

Sorry I cannot use my new phone properly. It is only the last sentence from my previoys entry that matters.

@Daimonion

"If you understand theory as philosophy of science or just science do, you're right."

(also an answer to halfgreek1963, thanks for this great cultural lesson).

Well, my guess is that the meaning that everyone has in mind, *today*, when hearing the word "theory" (not the same meaning, IMHO, as speculation, hypothesis, conjecture, etc). I'm open to dialog, but I have doubts about people thinking of the original greek meaning. 

This is called a conjecture by mathematicians.

The word has several meanings. Current usage is not confined to the specific scientific sense of a body of knowledge established by the empirical method of hypothesis, deduction and experiment.

The Greek origin is interesting and helpful, not because people use the word with that meaning today, but because it shows us the roots of today's usage. It lets us see the trajectory of the word through time.

The first meaning given by Chambers is 'an explanation or system of anything' and the next is 'an exposition of the abstract principles of a science or art'. 

In the case of chess, it means the body of knowledge which has been acquired through master practice and recorded for future use. This sense is clearly related to the scientific sense and also to the two meanings quoted from Chambers.

Another way to see it is to say that chess theory is what we can learn about the game by studying the work of others, as distinct from our own practice.

Why is "theory" called theory ?

In theory, if you elaborate a theory, it is theoretical action.

In theory, something you practice is practical.

the things you call theory are known as features. then there is opening theory, endgame theory etc and "a theory" such as "pink is better than blue" or "evolution is real".

There are 2 Theories of Chess: 

1. Classical - Control the center (d4, d5, e4, e5) by occupying it with your pawns and pieces

2. Hypermodern - Control the center by using the power of your pawns and pieces.  The advantage of this theory is that deprives your opponent of targets to attack in the center.

There are ancillary theories concerning advantages in space, time and material.  These are acquired with superior piece development, and superior pawn structure development.

Opening Theory is based on the above stated principles.

How is "pink is better than blue" comparable to "evolution is real" ?  

facepalm.

Are you facepalming over your own comment or what?  

[Even abbreviating is not allowed - Mod.] is wrong with you ?

Your comment makes zero sense.  That's [Even abbreviating is not allowed - Mod.] is wrong with me." 

maybe the comment wasnt meant for someone that has such a stupid problem with it.

Explain it then, prick.   

Manners, please.