French & Sicilian Identical Pawn structure

I have very little experience of either of these defences, but I have questions concerning both of them.

Although they start of very differently in nature, it seems to me that... A)_French defence with a later ...,c5; leads to the same black pawn structure as... B) Sicilian with ...e6; and ...,d5;.

How common is this crossover/transposition? If this black structure is likely to be reached, what are the pros and cons of each move order to get there?

Sincerely
Latent Potential

Transpositions between these two defenses are possible, but rarely happen. The Siciian generally appeals to players who like open positions. The French, to players who are more comfortable with closed or semi-closed positions since most main lines result in a center with pawns on e5 and d4 for White, e6 and d5 for Black. Play through some example games and you'll see what I mean.

Originally posted by Latent Potential
I have very little experience of either of these defences, but I have questions concerning both of them.

Although they start of very differently in nature, it seems to me that... A)_French defence with a later ...,c5; leads to the same black pawn structure as... B) Sicilian with ...e6; and ...,d5;.

How common is this crossover/transposition? I ...[text shortened]... ched, what are the pros and cons of each move order to get there?

Sincerely
Latent Potential

yes you can start with the Sicilian and end up with the French,

1. e4 c5 2. Nf3 Nc6 3. c3 e6 4. d4 d5 5. e5 Bd7 6. Be2


viola! Le French defence a la advanced variation!

While the pawn structures may end up similar, it only happens if white chooses to play that way. The sicillian is much more of an open game and french closed or semi-closed in most lines.

Originally posted by Latent Potential
...
Although they start of very differently in nature, it seems to me that... A)_French defence with a later ...,c5; leads to the same black pawn structure as... B) Sicilian with ...e6; and ...,d5;.

...Sincerely
Latent Potential

These are only similar if white chooses to play the 'closed" versions of the French or Sicilian, which are not that popular among better players. The main lines are not very similar, so I think the direct answer to your question is "Not too often, at least at the master level". But it does happen.

Open Sicilian 1. e4 c5 2. Nf3 e6 3 d4 cxd4 4 Nxd4
Main line French 1. e4 e6 2. d4 3 d5 3. Nc3 or Nd2

But if white plays 1. e4 c5 2. Nc3 e6 3. d3, you can also get very similar or identical positions to 1. e4 e6 2. d3 d5 3. Nc3.

As Robbie points out above, a lot of the 1. e4 c5 2. c3 e6 variations can also get positions that are similar or identical to positions out of the French. And if you are going to play c5 followed by e6, its best to know the French, too.

You can reach closed, solid, defensive and/or fairly passive positions from both openings depending on what variation you choose (see the games of Ulf Andersson). But for the aggressive player who wants open games, I doubt he would find the French defence sharp enough for his liking.