Anacrusis (pickup) is a bit more rhythmic than melodic. Hearing it seems easy to my musical brain, but I can understand how it would not be easy for others. Most music has a set rhythm, which we can understand in its simplest form by saying there is a fairly low number (most commonly 4), to which one can repeatedly count while listening to a piece of music, such that the piece will seem to flow with the counting.
Wait, what does that even mean? Let's use Happy Birthday as an example. If you count "one two three one two three one two three" repeatedly while someone is singing Happy Birthday, you'll hear/feel that the song seems to flow along with your counting, except you can't start the song with "one" right when the singer first says "Happy-". You have to start your count on "three" and then go back to "one", with the "one" matching when the word "Birthday" is sung. That's anacrusis. Here's a chart-like thing to hopefully make it more visual:
Count: 1 2 3 1 2 3 1 2 3 1 2 3
Singing: Happy birth-day to you Happy birth-day to...
So by now you're probably ready to ask, "Wait, why don't we just make 'one' fall on 'Happy' and then 'two' for 'birthday' and so on?" Excellent question, and this is the very core of anacrusis, and even rhythm in general. How do we know that it's a three-count? How do we know where the 'one' is?
Mainly, we feel it. When we sing Happy Birthday, we tend to naturally emphasize the syllables "birth-" and "you". Having the emphasis on the "one" is a popular component of rhythm, so it's a good bet when we are counting a song to put the "one" on emphasized syllables. That means we have to get a sense of the spacing between emphasized syllables (or beats) in order to know how high to count (e.g., "1 2 3 1 2 3" or "1 2 3 4 1 2 3 4", etc.).
To get back to the question at hand, how can you determine whether anacrusis is part of the music you are hearing?
- Understand that anacrusis (also called "pickup") only happens at the beginning of a piece.
- Determine the rhythm of the piece by guessing and counting and seeing if the "flow" seems to match the count. If it doesn't match, try a different count and/or a different "one".
- Go back to the beginning of the piece and find the first "one". If the melody matches or starts right after the first "one", there is no anacrusis. If the melody seems to come before the first "one", that could and would often be considered anacrusis.
That last phrase in step three is really what the articles you read seem to be about. Anacrusis could be in the eye of the beholder. Going back to the question of why we don't just count "one" on "Happy" in Happy Birthday, we could actually count "one" on "Happy" and then count sixes or twelves or even fours (which would create a different feel, sometimes called "three over four") and then we would not consider there to be anacrusis for Happy Birthday. Anacrusis and the rhythms we typically apply to music are merely conventions of western music theory, and other cultures can and certainly do develop theories and musical ideas that don't match, or even outright clash with the concepts that have their origins in western Europe and even back to ancient Greece.
So when talking among people who understand western music theory, you might describe a piece as having anacrusis, but if the artist(s) who composed and/or perform that piece don't see it that way, or don't even have that concept in their view of music, that is a valid point of view.
- Hey Jude by The Beatles (one on "Jude")
- Amazing Grace, traditional (one on the second syllable of "Amazing")
- Do You Hear The People Sing? from Les Miserables (one on "Hear")
- Tom's Diner by Suzanne Vega (one on the third "doo")
- Shake It Off by Taylor Swift (one on "late")
- I Feel Good by James Brown (one right after/on the second mora of "good")
- Symphony No. 5, start of first movement by Beethoven (one on the "duhn" of "dut dut dut duuhn....")
Here's a map of Mary Had a Little Lamb (non-blues children's version) to contrast with the Happy Birthday map above:
Count: 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
Singing: Ma- ry had a lit- tle lamb lit- tle lamb lit- tle lamb