Phrases, such as that one, need shape, direction, expression because they are communications from one human being to another. The medium is song (lieder), but it could be a solo instrument, or a small group of instruments or singers communicating among themselves and with the listeners. How does this expression occur? Not by singing the phrase flat and straight as I had undoubtedly been doing, but by lending it shape. Here is the phrase in question:
As you can hear, most of that phrase is simply repeated notes, mostly of the same rhythmic value. The expression is not clearly indicated (there is another version on YouTube, with the score, but missing, alas, the kind of expression I am talking about). The only dynamic is p. Everything that Wunderlich is doing in terms of expression, simply isn't in the score. But it is implied that you "do something with it". Now in some genres, such as the polka, this is simply not possible, nor desirable. We might generalize and say that all musical genres with a rigid tempo tend to rule out the kind of expression I am talking about. If you are playing polkas you don't want your fellow musicians "doing something with it". In that context it would probably be called "screwing around with the beat" and hence a bad thing. But in lieder, sonatas, most genres of classical music, it is so obvious that we don't even talk about it much, or do so indirectly.
There is a little less expression in even classical music than you would think because, frankly, not all classical musicians are actually 'musical' in the sense I am using the word here. By 'musical' I mean "capable of understanding, feeling and technically capable of communicating the musical expression that is implied by the melodic, harmonic and rhythmic qualities of the piece." This is what people mean when they accuse someone of "phoning in" a performance. The true expression isn't always there, though it is often faked, sometimes successfully. Similarly, in some non-classical genres, there are musicians who do have the ability to convey the necessary expression. Take Ringo, for example. George Martin is quoted as saying that Ringo wasn't the most consistent drummer, but he always seemed to vary the tempo in the right place. Well, duh! Ringo is almost unique as a drummer in that he really is with it musically. For him, unlike for most rock drummers, the tempo is not a rigid thing. Here, have a listen:
For most pop music and of course for all pop music with a drum track, which is pretty much all new pop music, the tempo is absolutely fixed and therefore INexpressive in the sense I am talking about. Now I don't mean dull or unexciting. The back-beat in rock music is strong and powerful, but it is mostly somatic, directed to the body. If I could confect a kind of ad hoc theory here, music directs itself to three possible human aspects: the head, the heart and the body. Dance music, from which rock music mostly comes, is about affecting the body. It makes you want to move. This doesn't exclude the head and the heart, but it downplays those aspects. If you want to reach the head and the heart, pure rock is not the ideal vehicle. In contrast, some music is very intellectual indeed. The big sets of variations I put up the other day by Bach and Beethoven are pretty intellectual as are most fugues and canons and quite a few of the more esoteric pieces of modern music. Music with a melting melody such as we find in Puccini operas, is directed mostly to the heart.
But some music achieves a kind of beautiful balance of all three of these aspects: the perfect example is the music of the Classical period. Haydn, Mozart and Beethoven can all write music that balances rhythmic verve, harmonic beauty and structure and graceful and expressive melodies. This is why I am a classicist, of course! What a wonder if you can integrate the melody, harmony and rhythm so as to appeal to the whole human person. If I were to develop this theory a bit, I might say that rhythm affects mostly the body, melody the heart and harmony the head. But it really isn't that simple. If you want to "do something" with a piece of music, i.e., make it the vehicle for true human expression, then you really have to make all the aspects work together.