I am not.
Nōn: not. Sum: I am.
I am with you.
Tēcum: with you (tē = you; cum = with). Sum: I am.
I am nothing.
More literally: I am none.
Less literally: I'm done for.
(To signify despair.) Nūllus /nūlla/nūllum (1/2, irreg.): not any, no, none. Sum: I am.
Are you a fool?
Stultus /stulta/stultum (1/2): foolish, stupid. Es: you are.
You are a conscientious fellow.
More literally: You are a dutiful man.
Officiōsus /officiōsa/officiōsum (1/2): attentive, dutiful. Homō, hominis (3m): man, human. Es: you are.
You are a great man.
Magnus /magna/magnum (1/2): great. Vir, virī (2m): man. Es: you are.
Ah, Brutus, where are you?
Ō (interjection): O! Oh! Brūte is the vocative singular form of the proper noun Brūtus, Brūtī (2m). Ubi (interrog. adv. —the i is sometimes long): where? Es: you are.
That is:
(The expression is common in English in its abbreviated form: i.e.,) Is/ea/ id (pron.): he, she, it; this, that. Est: is.
It is ridiculous.
Rīdiculus/rīdicula/ rīdiculum (1/2): amusing, funny; ridiculous, absurd. Est: it is.
Nothing is infinite except the Ocean.
Nihil (n, indeclinable, nom. or acc. only—here nom.): nothing. Īnfīnītus/īnfīnīta/ īnfīnītum (1/2): infinite. Est: is. Nisi (conj.): if not, unless; except. Ōceanus, Ōceanī (2m): ocean.
We are all wicked.
Omnēs is the m/f nominative plural form of omnis/omnis/omne (3): all; every. Malī is the masculine nominative plural form of malus/mala/malum (1/2): bad; evil, wicked. Sumus: we are.
We are, then, human beings.
Sumus: we are. Igitur (conj.): therefore, then. Hominēs is the nominative plural form of homō, hominis (3m): human, man.
We are dust and shadow.
Pulvis, pulveris (3m): dust. Et (conj.): and. Umbra, umbrae (1f): shadow. Sumus: we are.
You are just.
Iūstī is the masculine nominative plural form of iūstus/iūsta/iūstum (1/2): just. Estis: you are (pl.).
You are spies.
Explōrātōrēs is the nominative plural form of explōrātor, explōrātōris (3m): spy; explorer. Estis: you are (pl.).
Therefore you are poor.
Pauperēs is the m/f nominative plural form of pauper, pauperis (3, adj.): poor. Igitur (conj.): therefore, then. Estis: you are (pl.).
They are honorable.
Honestae is the feminine nominative plural form of honestus/honesta/honestum (1/2): honorable; noble; honest. (He’s talking about actions—āctiō, āctiōnis (3f): action; hence the feminine gender.) Sunt: they are.
They are slaves.
Servī is the nominative plural form of servus, servī (2m): slave. Sunt: they are.
There are none.
Nūlla is the neuter nominative plural form of nūllus/nūlla/nūllum (1/2, irreg.): no, none, not any. Sunt: there are.