Sententiae, Unit 11

7. Omnes idem sentiunt.

Omnes: masculine/feminine, plural, nominative, here used as a substantive adjective and is the subject of the main verb sentiunt

This is actually a third declension adjective which is discussed in Chapter 16. Omnis is the masculine/feminine nominative singular and omne is the neuter nominative singular. It is categorized as an adjective of "two endings". It's declension is as follows:
 

Idem: Neuter, singular, accusative. This is the neuter form of the personal pronoun is, ea, id. When the suffix -dem is attached to forms of the personal pronoun it becomes a demonstrative meaning the same (man, woman or thing depending on the gender). You would expect the neuter to be iddem but one d drops out and thus it becomes idem. The singular nominative forms of this demonstrative are: idem (masculine with a long i), eadem (feminine) and idem (neuter with a short i).

All men think the same thing.

11. Nec tecum possum vivere nec sine te.

possum: first person, singular, present, active, indicative (I am able) Remember that posse always takes a complementary infinitive to "complete" its meaning. The complementary infinitive in this sentence is vivere (which is a second conjugation verb because the e before the infinitive ending: re is long. To conjugate posse in the present future and imperfect active indicative tenses you simply attach the same tense of esse to the stem (either pos or pot). The stem will be pos before a form of esse that begins with an s and pot before the forms of esse which begin with a vowel. Hence the present, active, indicative of posse is:
 

I am able to live neither with you nor without you.

Martial was a writer of epigrams who lived in the last half of the first century C. E.