@talfan

Naturally, that is possible. Unfortunately I do not have a performance rating feature in my database, so I could not verify that the effect is real. I presumed, perhaps without foundation, that higher-rated Black players were more likely to play one of the critical lines of the BDG proper.  When I examine the set of games that transposed in this way, it appears to me offhand that Black is doing well.  For example, Black won all the games in which he was rated 2100 or under and White was rated 2101 or over. But perhaps this impression is mistaken after all.  

Of course, I would not let the statistics concern me if I were a BDG player.  I would simply learn a repertoire against the Classical French.  After all, White has a greater chance for theoretical advantage there, n'est-ce pas? Nor, as a habitual French player, would I give up the transposition if Black's performance rating were worse than in the usual French move order, since the French rewards those with long experience.

I remain curious, however, about whether our devoted BDG players contemplate this transposition with distaste, relish or indifference.

Re: BDG transposition to the Classical French

Sorry, I meant 3.e4 as corrected here:

Thank you.  Another fact supporting your point is that, if Black plays an Indian move-order, then after 1.d4 Nf6 2.Nc3 d5 3.e4 e6 it is really too late for the Alapin or Winckelmann-Riemer gambits, so a real red-blooded Classical French is in store for White. 4.Bd3 is hardly an exciting attacking line.

It also seems to me that instead 4.f3, as mentioned in my first post, has to be bad, since not only is Black not obligated to take the e-pawn, but f3 interferes with the defense of d4; then 4...c5 has to be good.

I agree to a large extent with MNb.  I don't have a problem when I play a BDG and my opponents "duck out" into a French Defence because I regularly play 1.e4 and the 3.Nc3 lines against the French.  But I imagine that many BDG-ers who are unfamiliar with 1.e4 lines will struggle.   It should be noted, though, that after 1.d4 Nf6 2.Nc3 d5 3.e4 e6, if Black wishes to head for a Burn Variation with 4.Bg5 dxe4, then 5.f3 is a reasonable attempt to transpose back to the Blackmar-Diemer.  Instead 4...Bb4 or 4...Be7 thwart the BDG-er.

We've had discussions before about attempted BDG transpositions after 1.d4 d5 2.e4 e6.  3.Be3 dxe4 4.f3, and 3.Nc3 Bb4 4.a3 Bxc3+ 5.bxc3 dxe4 6.f3, are slightly inferior to the standard BDG, while 3.c4?! and 3.Nc3 dxe4 4.f3?! (4...Bb4! -/+), are clearly unsound.

I think to play the BDG effectively with White, at the very least you need some knowledge of some of the Semi-Open Games after 1.e4 and a willingness to be flexible against the French in particular.

After 1.d4 Nf6 2.Nc3 d5 3.e4, Black can of course transpose directly to the stem position of the Classical French with 3...e6. Are BDG players really that well-prepared in the French? 

For BDG players: Do you see this often? What is your reaction on seeing this actually appear on the board? "Oh #!&%, I really never got around to studying this"? "Great, now I have a (generally accepted) theoretical advantage"? "Now I play f3 anyway"?

In my database Black has scored 53% when entering the Classical French(3...e6) from the BDG, as opposed to 46% when entering it normally from 1.e4.e6.  That's a striking example of the concrete effect of having more familiarity with the position than your opponent. On the other hand, among masters Black scores well over 53% when taking the e-pawn (in the BDG order).

However, among lower-rated players, I would think that the effect of unfamiliarity would be increased (since masters are at home in more types of positions) while the effectiveness of Black's lines accepting the gambit would be decreased (since non-masters have more trouble defending against gambits). This ought to render the transposition to the French more effective for lower-rated players than for masters.

Any thoughts on the pragmatic side of this matter?