In fact, all melody notes have some kind of tendency. And often a note will have more than one tendency.
A melody note having more than one tendency can be resolved many different ways. What makes one choice better than another?
Having played a short introductory series of notes at the beginning of an improvised phrase will surely bring you to a note that has many resolution options. Which one do you choose?
1. Newton's first law of melodic motion: "An ascending line tends to continue to ascend"
2. Newton's 2nd law of melodic motion: "A descending line tends to continue to descend"
3. On a strong beat the melody note tends to be a tone inside the current underlying chord.
4. The Surrounding Note Figure: If your melody line skips or jumps (any non-stepwise motion) there is a strong tendency to play the note in between the last two notes played immediately previous.
5. Cultural Factors: You are most likely to emulate the styles of music, phrasing and melodic features that you are most familiar with. A chinese musician will approach the subject of melody from a completely different viewpoint than, say, an Arabic or East Indian musician. Therefore the more Jazz you listen to, the more likely your lines are going to sound like Jazz.
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Whether or not you are consciously aware of the abovementioned factors, writing or improvising a melody is much like a game of chess.
Each melodic snippet brings you to a point where you have to make a melodic decision.
You have several choices facing you and any choice you make immediately offers several more choices until the phrase reaches its natural resolution.
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Only humans make music, and the very first melody instrument was the human voice. Ever since the invention of music, melody has been modeled on the human voice.
When creating a melodic phrase, keep in mind that the word "phrase" is a very specific term. It verifies the correlation between the spoken word and memorable, powerful melodic statements.
In the spoken language, the term "phrase" is effectively equal to the term "sentence".
A sentence has a logical beginning, perhaps a comma or two in the middle and a logical ending. Then the speaker TAKES A BREATH.
Melody closely follows the same structure.
Constantly ask yourself "Is this a 'sing-able' line?" If the answer is "Yes" then you have created a satisfying melody line.
If the answer is "No", then you are just twiddling around playing "finger patterns" that have no soul - because they HAVE NO INTENT and are ignoring the natural melodic tendencies.
This is why it gets boring very quickly listening to someone who has fantastic technique, yet no soul. And why greats like Basie and BB King can get so much impact out of very simple phrasings using an extremely limited number of notes.
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Remember to breathe! Even though your fingers have no need for air, the phrase itself does!
In order to teach phrasing, good teachers (and good students, too) will look to instruments that HAVE TO breath (horns, etc).