How can I tell the difference between a Petrarchan sonnet and an English/Shakespearean sonnet?

Petrarchan and English sonnets are very similar forms but have a few easy to spot characteristics that let you differentiate between them. The Petrarchan sonnet is the earliest sonnet form and consists of an octave (8 lines) and a sestet (6 lines) that make 14 lines in total. These will be in iambic pentameter and a Volta or turn will appear in the 9th line, beginning the sestet.In an English sonnet there are always 3 quatrains (4 lines) followed by a rhyming couplet. The Volta is found in the third stanza. This came later and was famously used by Shakespeare, therefore it is often referred to as a Shakespearean sonnet. Shakespeare alters the form slightly and places his Volta’s in the end couplet.