in reggae are less of a defining characteristic of the genre than the instrumentation and rhythm, as almost any song can be performed in a reggae style. However, it is very common for reggae to be sung in Jamaican Patois, Jamaican English, and Iyaric dialects. Vocal harmony parts are often used, either throughout the melody (as with vocal groups such as the Mighty Diamonds), or as a counterpoint to the main vocal line (as with the backing vocalists, the I-Threes). More complex vocal arrangements can be found in the works of groups like the Abyssinians and British reggae band Steel Pulse. An unusual aspect of reggae singing is that many singers use tremolo (volume oscillation) rather than vibrato (pitch oscillation). Notable exponents of this technique include Horace Andy and vocal group Israel Vibration. The toasting vocal style is unique to reggae, originating when DJs improvised spoken introductions to songs (or "toasts") to the point where it became a distinct rhythmic vocal style, and is generally considered to be a precursor to rap. It differs from rap mainly in that it is generally melodic, while rap is generally more a spoken form without melodic content. Lyrical themes Reggae is noted for its tradition of social criticism in its lyrics, although many reggae songs discuss lighter, more personal subjects, such as love and socializing. Many early reggae bands covered Motown or Atlantic soul and funk songs. Some reggae lyrics attempt to raise the political consciousness of the audience, such as by criticizing materialism, or by informing the listener about controversial subjects such as apartheid. Many reggae songs promote the use of cannabis (also known as herb, ganja, or sinsemilla), considered a sacrament in the Rastafari movement. There are many artists who utilize religious themes in their music – whether it be discussing a specific religious topic, or simply giving praise to God (Jah). Other common socio-political topics in reggae songs include black nationalism, anti-racism, anti-colonialism, anti-capitalism and criticism of political systems and "Babylon". In recent years, Jamaican (and non-Jamaican) reggae musicians have used more positive themes in reggae music. The music is widely considered a treasured cultural export for Jamaica, so musicians who still desire progress for their island nation have begun focusing on themes of hopefulness, faith, and love. For elementary children, reggae songs such as "Give a Little Love", "One Love", or "Three Little Birds", all written by Bob Marley,