sum et possum sum is an irregular verb

sum et possum

sum is an irregular verb. How do you remember the forms? You just do. The verb ‘to be’ is irregular in many languages. The principal parts of ‘to be’ are sum esse fuī futurus

present tense imperfect tense future tense sum eram erō es erās eris est erat erit sumus erāmus erimus estis erātis eritis sunt erant erunt NB – no macra in the present and future. There are macra in the past

esse is a linking verb. If you have a form of esse, watch out for predicate nominatives and predicative adjectives!

esse is used in many compound words. Remember adsum and absum? Here is another: posse. It is a compound of potis and esse. potis is an irregular adjective, meaning able/capable. posse means to be able.

present tense imperfect tense future tense possum poteram poterō potes poterās poteris potest poterat poterit possumus poterāmus poterimus potestis poterātis poteritis possunt poterant poterunt NB – the form should be po. Tsum, but the T changed to an S by assimilation

posse is used with a complementary infinitive (complere, to complete/fill). A complementary infinitive does not have its own subject; it has the same subject of the verb on which it depends.

agrōs bellōs vidēre nōn possumus. We are not able to see the beautiful fields. or We cannot see the beautiful fields. It is fine to translate posse as can, but I encourage you to translate it as be able. That way, the English grammatical structure matches the Latin grammatical structure (complementary infinitive).

Nōn amo tē, Sabidī, nec possum dīcere quārē. Hoc tantum possum dīcere: nōn amo tē. -an epigram by Martial

Nōn amo tē, Sabidī, nec possum dīcere quārē. Translation Step 1: What case is Sabidī? Translation Step 2: Translate non amo te. Translation Step 3: Translate nec possum dicere quare.

Hoc tantum possum dīcere: nōn amo tē. Translation Step 4: What is the subject of Hoc tantum possum dīcere? Translation Step 5: What is the main verb? What is the complementary infinitive? What is the object of that infinitive? What part of speech is tantum? Translation Step 6: Rearrange word order (ego) possum dicere tantum hoc. Translation Step 7: Translate non amo te.

Nōn amo tē, Sabidī, nec possum dīcere quārē. Hoc tantum possum dīcere: nōn amo tē. -an epigram by Martial I do not love you, Sabidius, nor am I able to say why. I am able to say only this: I do not love you.