I've read that one should know the tabia of an opening. And the way I understand it, a tabia is a certain (common) position some moves down one of the main lines of an opening. If this is correct, then my question is: how do I know when this so-called tabia occurs? Is it after 3 moves? 6 moves? 9 moves? 15 moves? Is it always after the same number of moves? I don't think so. And if so, what criteria tell me that the position is a tabia and not "just a position"? 

Thanks!

I don't there's any set in stone definiton so I can only tell you what my rudimentary understanding of the concept is.

In essence, a tabiya is any position that has occured in practice numerous times, where the opening branches out in a number of sub-variations. There's no set number of moves a tabiya occurs after, it depends on the opening.

Take the tabiya for the Closed Ruy Lopez for example, which occurs after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 d6 8.c3 O-O 9.h3. Black can now take the game on numerous different paths...Na5 (Chigorin), Nb8 (Breyer), Bb7 (Flohr-Zaitsev), Nd7 (Karpov) etc.

We pass a lot of branching points/tabiyas before getting to this position (Blacks 3rd move, Black's 5th, Whites 6th etc etc.) that will take you into variations with their own sets of tabiyas and ever on...But when someone says "Closed Ruy Lopez"...this is what you think of, the starting point of the Closed Ruy Lopez family of openings (if you're being pedantic, you could say the position after 7...d6 is the defining one, but since the moves that follow are played in the vast majority of games, we're not doing any harm).

So, yeah, basically it's just a branching position that occurs in practice alot and is thus familiar

Thank you, Arctor. But I still don't understand why some positions along the road are tabia, while others are not. In your example, you say the position is a tabia, since it occurs often in practice. Well, for this position to occur often, all other positions leading to this position must have occured often as well, but they are not (necessarily) considered tabia. So, what makes one position a tabia, and another not a tabia? 

 Ok, lets follow the Ruy Lopez example again, it wouldn't make sense to refer to any position before 7...d6 as the tabiya for the closed Ruy Lopez because Black can still go into multiple different lines that are not the closed Lopez (he can play the Open Lopez with 5...Nxe4, he can play 7...Bb7, he can play the Marshall Attack with 7...O-O and 8...d5 etc etc.).

The next moves after 7...d6 are, almost invariably, 8.c3 0-0 (other alternatives are so offbeat and rare relative to the main line that they're hardly worth consideration).

White does have a choice now (he can play 9.d3 or 9.d4 for example) but theory has dictated that 9.h3 is the best try for an advantage and thus it is overwhelmingly the most played move. Blacks choice isn't so clear however and he has multiple good moves (they'll lead to different types of games, but none is objectively better than the others (at least not for our purposes)) so this is the perfect place to stop and label the position as one of note...a tabiya

So what makes one position a tabiya, while another one (which could be only a move previous) is not? The importance of the branches I guess...

So a tabia is any (opening) position where the player to move has a valid choice to make? Would that be a meaningful definition? Obviously there is always plenty of choices. For example, after 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5, White could play any one of the 25 legal moves. However, only one of them (7. Bb3) makes any sense. Therefore, this is not a tabia, since the next move really isn't a choice, since it's more or less dictated. But after 7. Bb3, Black has a choice to make (most likely between 7...d6 and 7...O-O), and we're now at a crossroad - at a tabia. Does this sum up the concept of a tabia? 

tabiya

Interesting, pellik! Yes, that makes it easier to understand the idea. Great info! 

paulgottlieb, so you agree with my explanation (post #5), right? 

Looking in the Game Explorer, I sense one could use the stats to tell if the position is a tabia or not. After the 3. move, in this move sequence - 1.e4 e5 2.Nf3 Nc6 3.Bb5 a6 4.Ba4 Nf6 5.O-O Be7 6.Re1 b5 7.Bb3 d6 8.c3 O-O 9.h3 (the Roy Lopez) - all moves along the way are almost "automatic", except for a few. Those few ones, where a choice is to be made, I guess is the tabia. We can actually use the numbers in the database to give us a hint as to when a tabia occurs (assuming that what people have said so far is correct, and that I understand it correctly). Here's how... 

At every move we can look at how often the moves are played. If one of all the possible replies is much more common than all the others, it's not a tabia, since "no choice" has to be made.

At move 4, 5, 6 and 8 in the line above, the most common move is much more common than all other replies, appearing in 70-100 % of all games in the database, with the second most common move trailing way behind (being played in 14 % or less of all the games).

But at the 7. and 9. move it's different for Black. Here Black has a choice to make, as reflected in the stats. At the 7. move, Black's most common reply (d6) is played in 63 % of all the games, while the second most common move (O-O), is played in 37 % of the cases. A choice has to be made, and so this is a tabia. Even more pronounced is Black's 9. move - as paulgottlieb pointed out - as the most common reply from Black (h3) is only played in 46 % of the master games, while the second most common reply (Nb8), and the third most common reply (Bb7), is played in 19 % and 13 % of the games, respectively. Again a choice is to be made, and again we are at a tabia. 

Further, at Black's 9. move, there are plenty of other moves accounting for a decent share of the replies at this point. 

If I'm right, we can actually use the stats to help us get a hint as to what is, and what isn't, a tabia. Would you agree? Does this make any sense? 

A tabya is a position that someone thinks is a useful starting point for opening preparation. It's not an objective thing.

kwaloffer, really? It actually makes sense, since I remember GM Soltis talking about "positions he liked", and I think he was referring to them as tabia.

The way I interpret tabiya is a position for which a LOT of study will have a leveraged impact on your entire chess game, not just on that one position.

An alternate, more practical version is that it is a position which, despite years and many grandmaster games, is still open to further study.

Another interesting definition. But now I have to ask, what criteria makes one position such a position?

Tabiya (= huge jug):

I'm pretty sure the tabia is part of the female anatomy.

Could you be thinking of Tabitha?

Seriously...

Is there a collection of tabiyas anywhere (book or net)?

Dnell, thanks.

Tabia is not a part of either male or female anatomy. Tibia and labia are, though.

Nice.