Does the Reti always have to transpose into something else or can it remain as a substantive line?

Thanks, the reason i raised the subject was because i was very surprised to see it was the 3rd most popular opening after e4 and d4.

1.Nf3 is indeed the 3rd most popular first move but "The Reti" is not even the 7th most popular opening. You will not surprise if you realize that many openings have Nf3 in it. It is just not the first move. For example, 1.d4 d5 2.Nf3 is equivalent with 1.Nf3 d5 2.d4. (You are not thinking that anything with 1.Nf3 is a Reti opening, are you? Because if it is so then a KID can be a Reti as well)

No i know about the Kings Indian, i was generally puzzled because BATSFORD CHESS OPENINGS 2 has little to say about the Reti, just its possibilities to transpose, describing it as shy, flexible.

It seems all about keeping your opponent guessing.

The Reti is very rare and largely unused so you won't find too much on it. The Reti proper is 1.Nf3 d5 2.c4. If Black takes then 3.e4, 3.Na3 and 3.Qa4+ are the usual moves.

If Black plays 2...d4 then White has lots of reversed openings he can use like the reversed benko gambit or reversed benoni.

After 2...e6 or 2...c6 White can transpose to other things or still play Reti style with b3 thrown in.

Thanks.