What is the difference between a Recitative and an Aria in Baroque Opera?

Recitatives and Arias serve two contrasting functions in the Baroque Opera.

A recitative, also known by the Italian name 'recitativo', acts as a dialogue and allows the characters to move the story onwards through a narrative. Recitatives are generally accompanied by solely the basso continuo which provides a sparser texture and are written in speech like rhythm. A clear example of a baroque recitative can be seen in "Adonis Will Not Hunt Today" from Venus and Adonis. Note here the iregular rhythms and non melodic melody.

An Aria on the other hand is a display piece for the virtuosic soloist. This acts to display the vocal skills of the singer and rather than moving the narative on it pauses the movement of the story for the character to focus on a singular emotion. Clear features of an Aria are expressive word painting, melisma and extensive ellaboration. An example of this can be seen in "When I am Laid in Earth" from Dido and Aeneas. Notice here the repetivite nature of the lyrics and the more melodic lines as well as the emotive use of appogiatura and ornamentation.