A corporeal Patronus is one that is fully-formed, taking the shape of bright-white, translucent animal. The specific animal forms that corporeal Patronuses take vary from person to person and reflect each individual's personality.
Patronus forms, however, are subject to change if the caster goes through an emotional upheaval of some sort, including falling in eternal, unchanging
love.
[13] For example,
Nymphadora Tonks's Patronus changed from its previous form to that of a four-legged creature which others guessed was a
werewolf because then it would reflect her love of
Remus Lupin, himself a werewolf.
[9] Another example is
Severus Snape, whose Patronus was that of a doe, the same as
Lily Evans, though this may have been the case all along rather than a change from its original form, as Snape was in love with Lily for most of his life. Based on the fact that Patronuses are conjured by recalling happy memories, it stands to reason that a Patronus might change its form after one falls in love and the memories used to conjure the Patronus largely revolve around the person the caster is in love with. In addition, it seems that some couples have "complementary" Patronuses (male and female forms of the same animal), such as Lily and
James Potter. It is, however, unknown if this is a coincidence or not. If a wizard is an
Animagus and can summon a corporeal Patronus, the two may take the same form, as was the case for
Minerva McGonagall and James Potter.
[10]