Here's one that's always perplexed me a bit.

Standard feather step 2: LF fwd L shoulder leading
Feather ending step 2: LF diag fwd

Any ideas on why these positions need to be different in the two cases would be appreciated. Thanks.

In the first case ("Standard" feather step), there is no turn (i.e., alignment doesn't change).

In the second case (Reverse turn with feather ending in foxtrot?), the leader is on the inside of a reverse turn when approaching the feather ending, hence the diag fwd (ISTD manual and Alex Moore's Ballroom Dancing: "left foot to side and slightly forward").

There is a curve to the right on the Feather Step. The name that should be used on 4 5 6 of a Reverse Turn is a Feather Finish.
As pointed out by Terence the term no longer used is left shoulder leading. On the Feather Step on step two we turn sideways and we step through O/S lady with no change in the shape on step three. This is called CBMP on step three.
In a Reverse Turn on steps 4 5 6 the lady is on the outside of the step and has further to go. The man must let her pass.

is there - all steps are on the same alignment ?

">There is a curve to the right on the Feather Step.

is there - all steps are on the same alignment ?"

The curve in travel shows up between the feather step and the following figure. Steps 1-3 of the feather may fall on a common line, but the next step cannot be on that same line, it has to go to the right of it.

In essence, this is because step 3 is simply forward in CBMP and not forward "and across" in CBMP.

If you dance feathers and three steps in sequence, there's a little 'dog leg' introduced at the end of the feather and counteracted in the three step. Turned around backwards and danced as the more popular continuous waves, this gives the characteristic sinuous path.

Suggest looking at the diagram in "Ballroom Dancing" to get an idea of how there can be curve without turn.

anonymous. On a Feather Step there should be a curve to the right, not a turn. If there isn't you could resemble a batting ram.
If you look at the charts and also go to Sway you will find that it is written that there is Sway on figures that curve and wave. On the Feather Step there is Curve and Sway to the Right on two and three.
One theory is that when the Feather was actually a cross up behind some individual decides that something that resembled a Close Change step which they turned to face diagnal to the centre felt much better if the foot passed instead of closing. Thus the Feather Step might have been born.That would have been about 1920

"On a Feather Step there should be a curve to the right, not a turn."

Serendipity, once again you fail to actually read the post your are responding to. If you had read it, you would have seen:

"Suggest looking at the diagram in "Ballroom Dancing" to get an idea of how there can be curve without turn."

Paul . So you do still think that there is no curve to the right on a Feather Step in the Foxtrot according to the charts
The third step of the Feather is not on a common line. In the chart it can be clearly seen that is travelling in a different direction to step two.