amatus or amatum - which one is the perfect passive participle form

Question

I've just started studying Wheelock. In the Vocabula section, the entry for amo is amo, amare, amavi, amatum. Yet most dictionaries give the past participle as amatus. Which is correct?

Answer 1

Both are correct. The perfect participle has several forms for different genders, numbers, and cases. An entry in a dictionary does not give all the forms of a word, not even all the forms of any participle of a verb, but enough hints that allow you to figure out all the forms. For the perfect passive participle the typical choice is to list the singular nominative in either masculine or neuter. The plural feminine accusative amatas would serve the purpose just as well, so this is more a matter of tradition than of logic.

See also:

• Why is the first person singular the citation form?
• Why do some sources give the principal parts in a different order, or include an extra, fifth principal part?
• Dictionaries always list the Neuter Participle in principal forms, why?
• Three forms of a Latin verb?
• Why are verbs often listed under their first person singular form and not under infinitive as in many other languages?

Answer 2

In the context of vocabulary lists, amatum can be interpreted as the neuter of the perfect passive participle (as per Allen and Greenough), but it can alternatively be interpreted as the accusative supine form. Supines are more rarely used in general than perfect passive participles, but some verbs that lack passive forms have a supine. They have the same stem, and the stem is the important part when giving a principal part of a verb: it doesn't make a difference what the ending is because you have to take that off anyway to form other forms of the verb.

Sometimes the future active participle is listed instead: this is a third form built on the same stem.