The regular verbs are classes into three groups 'ar', 'er' and 'ir'
Slide 2
Irregular verbs
There are some classes within the irregular verbs which, themselves, demonstrate patterns
Radical stem changing verbs with an 'o' e.g. poder: puedo, puedes, puede etc
Radical stem changing verbs with a 'e' e.g. pensar: pienso, piensas, piensa etc.