A music genre is a conventional category that identifies some pieces of music as belonging to a shared tradition or set of conventions. It is to be distinguished from musical form and musical style, although in practice these terms are sometimes used interchangeably. Academics have argued that categorizing music by genre is inaccurate and outdated.
Music can be divided into different genres in many different ways. The artistic nature of music means that these classifications are often subjective and controversial, and some genres may overlap. Academic definitions of the term genreitself vary. In his book Form in Tonal Music, Douglass M. Green distinguishes between genre and form. He lists madrigal, motet, canzona, ricercar, and dance as examples of genres from the Renaissance period. To further clarify the meaning of genre, Green writes, "Beethoven's Op. 61 and Mendelssohn's Op. 64 are identical in genre—both are violin concertos—but different in form. However, Mozart's Rondo for Piano, K. 511, and the Agnus Dei from his Mass, K. 317, are quite different in genre but happen to be similar in form." Some, like Peter van der Merwe, treat the terms genre and style as the same, saying that genre should be defined as pieces of music that share a certain style or "basic musical language." Others, such as Allan F. Moore, state that genre and style are two separate terms, and that secondary characteristics such as subject matter can also differentiate between genres. A music genre or subgenre may also be defined by the musical techniques, the cultural context, and the content and spirit of the themes. Geographical origin is sometimes used to identify a music genre, though a single geographical category will often include a wide variety of subgenres. Timothy Laurie argues that, since the early 1980s, "genre has graduated from being a subset of popular music studies to being an almost ubiquitous framework for constituting and evaluating musical research objects".
Alternatively, music can be assessed on the three dimensions of "arousal", "valence", and "depth". Arousal reflects physiological processes such as stimulation and relaxation (intense, forceful, abrasive, thrilling vs. gentle, calming, mellow), valence reflects emotion and mood processes (fun, happy, lively, enthusiastic, joyful vs. depressing, sad), and depth reflects cognitive processes (intelligent, sophisticated, inspiring, complex, poetic, deep, emotional, thoughtful vs. party music, danceable). These help explain why many people like similar songs from different traditionally segregated genres.
Art music primarily includes classical traditions, including both contemporary and historical classical music forms. Art music exists in many parts of the world. It emphasizes formal styles that invite technical and detailed deconstruction and criticism, and demand focused attention from the listener. In Western practice, art music is considered primarily a written musical tradition, preserved in some form of music notation rather than being transmitted orally, by rote, or in recordings, as popular and traditional music usually are. Historically, most western art music has been written down using the standard forms of music notation that evolved in Europe, beginning well before the Renaissance and reaching its maturity in the Romantic period. The identity of a "work" or "piece" of art music is usually defined by the notated version rather than by a particular performance, and is primarily associated with the composer rather than the performer (though composers may leave performers with some opportunity for interpretation or improvisation). This is so particularly in the case of western classical music. Art music may include certain forms of jazz, though some feel that jazz is primarily a form of popular music. The 1960s saw a wave of avant-garde experimentation in free jazz, represented by artists such as Ornette Coleman, Sun Ra, Albert Ayler, Archie Shepp and Don Cherry. And avant-garde rock artists such as Frank Zappa, Captain Beefheart, and The Residents released art music albums.
Popular music is any musical style accessible to the general public and disseminated by the mass media. Musicologist and popular music specialist Philip Tagg defined the notion in the light of sociocultural and economical aspects:
Popular music, unlike art music, is (1) conceived for mass distribution to large and often socioculturally heterogeneous groups of listeners, (2) stored and distributed in non-written form, (3) only possible in an industrial monetary economy where it becomes a commodity and (4) in capitalist societies, subject to the laws of 'free' enterprise ... it should ideally sell as much as possible.
Popular music is found on most commercial and public service radio stations, in most commercial music retailers and department stores, and in movie and television soundtracks. It is noted on the Billboard charts and, in addition to singer-songwriters and composers, it involves music producers more than other genres do.
The distinction between classical and popular music has sometimes been blurred in marginal areas such as minimalist music and light classics. Background music for films/movies often draws on both traditions. In this respect, music is like fiction, which likewise draws a distinction between literary fiction and popular fiction that is not always precise.
Rock music is a broad genre of popular music that originated as "rock and roll" in the United States in the early 1950s, and developed into a range of different styles in the 1960s and later, particularly in the United Kingdom and in the United States.
Soul music became a musical genre that came to include a wide variety of R&B-based music styles from the pop R&B acts at Motown Records in Detroit, such as The Temptations, Marvin Gaye and Four Tops, to "deep soul" singers such as Percy Sledge and James Carr.
Country music, also known as country and western (or simply country) and hillbilly music, is a genre of popular music that originated in the southern United States in the early 1920s.
Hip hop music
Hip Hop music, also referred to as hip hop or rap music, is a genre of music that was started in the United States, specifically the South Bronx in the New York City by African-American youth from the inner cities during the 1970s. It can be broadly defined as a stylized rhythmic music that commonly accompanies rapping, a rhythmic and rhyming speech that is chanted. Hip hop music derives from the hip hop culture itself, including four key elements: emceeing (MCing)/rapping, Disc jockeying (DJing) with turntablism, breakdancing and graffiti art.
The polka is originally a Czech dance and genre of dance music familiar throughout Europe and the Americas.
Religious music (also sacred music) is music performed or composed for religious use or through religious influence. Gospel, spiritual, and Christian music are religious music.
Traditional and folk music
Traditional and Folk music are very similar categories. Although the traditional music is a very broad category and can include several different genres, it is widely accepted that traditional music encompasses folk music. According to the ICTM (International Council for Traditional Music), traditional music are songs and tunes that have been performed over a long period of time (usually several generations). 
The Folk music genre is classified as the music that is orally passed from one generation to another. Usually the artist is unknown, and there are several different versions of the same song. The genre is transmitted by singing, listening and dancing to popular songs. This type of communication allows culture to transmit the styles (pitches and cadences) as well as the context it was developed.
Culturally transmitting folk songs maintain rich evidence about the period of history when they were created and the social class in which they developed. Some examples of the Folk Genre can be seen in the Folk music of England and Turkish Folk music. English folk music has developed since the medieval period and has been transmitted from that time until today. Similarly, Turkish Folk music relates to all the civilizations that once passed thorough Turkey, thereby being a world reference since the East-West tensions during the Early Modern Period.
Traditional Folk music usually refers to songs composed in the 20th century, which tend to be written as universal truths and big issues of the time they were composed. Great names such as Bob Dylan; Peter, Paul and Mary; James Taylor; and Leonard Cohen transformed Folk music to what it is known today. Newer composers such as Ed Sheeran (Pop Folk) and The Lumineers (American Folk) are examples of Contemporary Folk music, which has been recorded and adapted to the new way of listening to music (online)—unlike the traditional way of orally transmitting music.
Each country in the world, in some cases each region, district and community, has its own Folk Music style. The different sub-divisions of Folk genre are developed by each place, cultural identity and history. Because the music is developed in different places, a lot of the instruments are characteristic to location and population—but some are used everywhere: Button or Piano Accordion, different types of flutes or trumpets, Banjo, and Ukulele. Both French and Scottish folk music use related instruments such as the Fiddle, the harp and variations of bagpipes.
Emergence of new genres and sub-genres
New genres can arise by the development of new forms and styles of music and also simply by creating a new categorization. Although it is conceivable to create a musical style with no relation to existing genres, new styles usually appear under the influence of pre-existing genres. The genealogy of musical genres expresses, often in the form of a written chart, the way in which new genres have developed under the influence of older ones. If two or more existing genres influence the emergence of a new one, a fusion between them can be said to have taken place. The proliferation of popular music in the 20th century has led to over 1,200 definable sub-genres of music.
Psychology of music preference
Social influences on music selection
Since music has become more easily accessible (Spotify, iTunes, YouTube, etc.), more people have begun listening to a broader and wider range of music styles. In addition, social identity also plays a large role in music preference. Personality is a key contributor for music selection. Someone who considers themselves to be a "rebel" will tend to choose heavier music styles like Heavy Metal or Hard Rock, while someone who considers themselves to be more "relaxed" or "laid back" will tend to choose lighter music styles like Jazz or Classical music. There are five main factors that exist that underlie music preferences that are genre-free, and reflect emotional/affective responses. These five factors are:
A Mellow factor consisting of smooth and relaxing styles (Jazz, Classical, etc.).
A Sophisticated factor (Operatic, World, etc.)
An Intensity factor that is defined by forceful, loud, and energetic music (Rock, Metal, etc.).
A campestral factor, which refers to singer-songwriter genres and country.
Individual and situational influences
Age is another strong factor that contributes to musical preference. Evidence is available that shows that music preference can change as one gets older. A Canadian study showed that adolescents show greater interest in pop music artists while adults and the elderly population prefer classic genres such as Rock, Opera, and Jazz.
Genealogy of musical genres
List of music styles
List of popular music genres
List of radio formats