Music theory is the language of pskovmusic.ru. Those who understand the language of music, those who can read and write music are called musicians. Just as people who share a common language communicate everyday, musicians communicate through a common musical language.
The language musicians communicate in is not by speaking but rather by the use of sheet music. Sheet music contains information that allows musicians to play the same piece of music on their instruments regardless of which language they speak. People all around the world communicate through the language of music and that is why music is called the universal language.
2) Do I need to know music theory in order to play a musical instrument?
This is a tricky question and the answer is yes and no. Allow me to explain. If some noise or sound has rhythm, a melody, and harmony, it can be called music. Without these components it is simply noise or organized noise.
A musician, someone who understands music theory and is able to communicate in the language of music, will compose a piece of music and know what they are doing and why they are doing it. A musician will know the name of the notes, chords, and scales they are using and more important, they will know why the musical composition works or sounds good.
A musician does not need to hear the musical composition to know wether or not certain notes and chords sound good when played together, because the theory has already determined what note and chord families will sound good together and why it is so.
On the other hand many people who play music, do play by ear. Many of those who play by ear do not know the name of the notes, chords, and scales they are playing, yet they are able to create a musical composition that is pleasing to the ear of the listener.
Players who learn and create music by ear have developed a good sense of pitch and as they continue to train their ear, their ability to identify notes, chords, and qualities of chords, will improve.
Typically, those who play by ear are limited to playing simple forms of music like blues, rock, pop, and country. It is very difficult to play classical and jazz music without some form of musical training and a decent grasp on music theory.
People who have the ability to learn complex forms of music by ear have an extraordinary musical gift and they might even be considered musical prodigies.
To help draw a distinction between musicians and those who play music by ear I offer this example. A person who uses a computer may not have a clue about how a computer works, yet they can type a letter, send an e-mail, or surf the net. The same is true with music.