The Wikipedia article on 2017 WTA Finals1 has some brief explanation of how qualification for this tournament works. Based on the description given there it seems that simply the top players in the race rankings are taken. (The only thing which is slightly more complicated is which tournaments have to be counted, it seems that they are Grand Slams and some Premier level tournaments, with some possible exceptions.2
Apart from rankings, are there some other conditions player has to fulfill to qualify?
- For example, in the men's tournament3, Grand Slam winner might qualify even if he is not in the top 8 positions of rankings. Is there a similar rule for WTA finals? (Of course, it is already clear that this cannot happen in ATP rankings this year. But if you look at WTA rankings, the US Open winner Sloane Stephens missed the first half of the season due to surgery, so she is very unlikely to get into top 8. So if there is a similar rule also for WTA finals, it could make difference.)
- Another example: In an online discussion, I was told that one of the condition for qualifying is that the player has to win at least one WTA tournament during the year. However, I was not able to find any confirmation of this rule. (And this would contradict the Wikipedia article - Venus Williams is listed among players who already qualified, but so far she does not have a WTA title in this season. Of course, what somebody claims online is far from being a reputable source, but still that made me curious.)
1Here is link to the current revision.
2Some exceptions concerning the premier tournaments are mentioned in the footnotes below the table saying: "The player's ranking at the time did not qualify her to play this event. Accordingly, the player's next best result is counted in its place." and "The player was not a Top 20 player at the end of 2016 and therefore not required to count her two best Premier 5 results. Accordingly, the player's next best result is counted in its place."
3Again, I will add a link to the current revision of the Wikipedia article.