For example, I don't remember what words he used to explain to us that in a score, you have to communicate clearly who plays what. It's obviously not a problem in solo piano music, nor even in string quartet music.
There are two violins in a string quartet, and they should always get separate staves. So in Wolfgang Amadeus Mozart's Quartet in G major, K. 387, when the first violin is silent for several consecutive measures, the whole rests in the first violin's staff readily convey to us that it is the second violin that is playing now, along with the viola and cello.
In orchestral music, when you have ten or twelve first violins, it would hardly make any sense to use ten or twelve separate staves if they're playing in unison the vast majority of the time. It is with the wind instruments (and by that I mean both woodwinds and brass) that clarity of part assignment requires a great deal of painstaking care.
Generally, when you have an orchestra with woodwinds in pairs, each pair shares a staff. This means two flutes on one staff, two oboes on one staff, and so on and so forth, down to maybe two tenor trombones on one staff, and perhaps even bass trombone and tuba share a staff even though they're different instruments.
Let's say this is a staff for two oboes:
Clearly first oboe plays E-flat and second oboe plays C-sharp. No problem. But what if then we have this?
Both first oboe and second oboe are to play a unison D, right? I think they're smart enough to figure it out in rehearsal. But enough details like that, and the rehearsal gets bogged down in things the composer or arranger should have taken care of beforehand.
This would be clearer:
Of course the score and parts should all print out in black ink. I am using direct screenshots from the notation software to underscore the point that these are things for the composer or arranger to mind, not the performers.
It would be even clearer, if, in addition to the stems pointing opposite ways, you add "a 2" or "zu 2" above that.
You might say that this is a toy example. And it is. In Finale 2010 and later (and maybe some earlier versions, too), you can set up linked parts so that the computer will automatically take the top note of the chord and give it to the first player, and give the bottom note of the chord to the second player.
You want to review the parts when you use this feature, there might be occasional mix-ups. But this toy example with the two oboes would present no problem whatsoever. The two oboists would probably not be aware of any issue at all.
Still, this toy example is very typical of situations you will come across if you do even just a little arranging for orchestra or wind symphony. Now I will present a more interesting example, a situation that you may or may not ever come across.
I have mentioned before my ongoing work on orchestrating Clara Schumann's Scherzo in D minor. I might still tweak the instrumentation a little bit, but for the most part, the task ahead of me consists of boring but important details like making sure there are dynamics markings (piano, mezzo-forte, etc.) everywhere they are needed.
There is a passage early in the piece that is obviously a repeat. I don't know if Schumann used repeat signs in her original score but the publisher wrote out the repeat, or if she wrote out the repeat and the publisher didn't second-guess her.
More likely the latter. Anyone who has turned pages for a pianist will probably advise a composer that repeats are a bad idea for solo piano music. It's different in orchestral music. If a section to be repeated takes up, say, half a page on a player's part, it makes perfect sense to use repeat signs. It might even simplify the problem of page turns.
Of course I had the option of orchestrating the passage in question differently the second time around. But I chose to orchestrate it the same both times, and so repeat signs make sense. Going into the repeat, the first clarinet is playing this:
Hmm, that first diminuendo "hairpin"is a little too close to the eighth notes' shared beam. Another one of those boring details I have to work on. Anyway, a few measures back I put in a "1." to indicate that I intend the first clarinet to play this.
Maybe I should add another "1." right after the begin repeat sign, just to be absolutely clear. But this is what I have coming out of the repeat:
I might want to add a redundant sharp for the second clarinet's D-sharp, just in case the notation software neglects to put it in... or the conductor thinks I meant to have the second clarinet play D-natural.
So... for the first clarinet going through this section the second time, the piano marking might seem redundant. But we expect our second clarinet to play that D-sharp leading to E-natural and then not play the E-natural when we go back to the beginning of the repeated section? Wait a minute: this is a lot like the toy example for the oboes, but transposed!
Writing out a repeated section just because of this little detail seems overkill to me. I think what I'm gong to do, unless I get better advice, is to add "a 2 la seconda volta" at the beginning of the repeated section.
It's certainly possible to bypass these problems by giving separate staves to each and every one of the wind instruments. I've seen at the Detroit Public Library a score of Basile Kalinnikov's Symphony No. 1 in G minor that does precisely that.
The problem with that approach is that, unless you're Leonard Bernstein, it becomes a little difficult to quickly ascertain which instrument is playing a certain line. It would be completely understandable if the conductor confused a second oboe for a first clarinet. I know that sort of thing would happen to me if I was on the podium.
There are no shortcuts here. As a composer or arranger, I must put myself in the shoes of the conductor and the players, and do everything I can to clearly communicate details such as these, not leave them to the musicians to figure out at rehearsal.