Mihi: to me—the dative form of ego: I. Quidem (particle): at any rate; indeed. In (prep.): (with abl.) in, on; (with acc.) into. Tōtā is the feminine ablative singular form of tōtus/tōta/tōtum (1/2, irreg.): whole, entire, total, all. Ratiōne is the ablative singular form of ratiō, ratiōnis (3f): reason; rationale; doctrine, theory. Eā is the feminine ablative singular form of is/ea/id (adj.): this, that. (To me at any rate, in this whole doctrine. . .)
Quī/ quae /quod (rel. pron.): who, which, that, what. Pertinet is the third person singular form of pertineō, pertinēre, pertinuī, — (2): to pertain, relate, apply, affect. Ad (prep.): to (takes the accusative). Animus, animī (2m): mind, soul. Perturbātiōnem is the accusative singular form of perturbātiō, perturbātiōnis (3f): confusion, disturbance, disorder. (. . . which relates to the disorder of the mind. . .)
Ūnus/ ūna /ūnum (1/2, irreg.): one; alone; only, sole, single. Rēs, reī (5f): thing; matter, affair. Vidētur is the third person singular passive form of videō, vidēre, vīdī, vīsum (2): to see; (in the passive) seem. Causam is the accusative singular form of causa, causae (1f): cause; case; situation; matter, subject. Contineō, continēre, continuī, contentum (2): to hold together; connect; contain, comprise, comprehend in itself. (. . . one thing seems to comprehend the matter in itself. . .)
Omnēs is the m/f accusative plural form of omnis/omnis/omne (3): all; every. Eās is the feminine accusative plural form of is/ea/id (pron.): he, she, it; this, that. Esse: to be. In (prep.): (with abl.) in, on; (with acc.) into. Nostrā is the feminine ablative singular form of noster/nostra/nostrum (1/2): our, ours. Potestāte is the ablative singular form of potestās, potestātis (3f): power, ability; control; authority. Iūdiciō is the ablative singular form of iūdicium, iūdiciī (2n): judgment, opinion; decision, choice. Susceptās is the feminine accusative plural form of susceptus/suscepta/susceptum (1/2), the perfect passive participle (taken up) of suscipiō, suscipere, suscēpī, susceptum (3, –iō): to take up; acknowledge; accept. Voluntāriās is the feminine accusative plural form of voluntārius/voluntāria/voluntārium (1/2): voluntary. (. . . them all to be—i.e., that they all are—in our control, all taken up by opinion/by means of judgment, all voluntary.)
Hic /haec/hoc (adj.): this. Igitur (conj.): therefore, then. Error, errōris (3m): wandering; error. Est: is. Ēripiendus /ēripienda/ēripiendum (1/2) is the gerundive (to be torn out) of ēripiō, ēripere, ēripuī, ēreptum (3, –iō): to pull or tear out, snatch away. Ēripiendus est is the passive periphrastic: must be pulled out, etc. (This error, then, is to be torn out. . .)
Hic/ haec /hoc (adj.): this. Dētrahendus/ dētrahenda /dētrahendum (1/2) is the gerundive (to be removed) of dētrahō, dētrahere, dētrāxī, dētractum (3): to remove, strip. Opīniō, opīniōnis (3f): opinion; belief. (. . . this opinion to be removed. . .)
Atque /ac (conj.): and, and also, and then. Ut (rel. adv.): just as. In (prep.): (with abl.) in, on; (with acc.) into. Malīs is the ablative plural form of malum, malī (2n): a bad thing; evil; trouble, misfortune. Opīnātīs is the m/f/n ablative plural form of opīnātus/opīnāta/opīnātum (1/2), the perfect passive participle (imagined, judged) of opīnor, opīnārī, opīnātus sum (1, deponent): to think (perfect participles of deponent verbs usually have an active meaning, but they do occasionally have a passive one, like here). Tolerābilia is the neuter nominative plural form of tolerābilis/tolerābilis/tolerābile (3): endurable, tolerable (it connects to efficienda in the next part of the sentence). (. . . and just as in imagined bad things/in things believed bad (things must be made) tolerable. . .)
Sīc (adv.): so, thus. In (prep.): (with abl.) in, on; (with acc.) into. Bonīs is the ablative plural form of bonum, bonī (2n): a good thing, a good. Sēdātiōra is the neuter nominative plural form of sēdātior/sēdātior/sēdātius (3): calmer—the comparative form of sēdātus/sēdāta/sēdātum (1/2): calm (originally the perfect passive participle of sēdō, sēdāre, sēdāvī, sēdātum (1): to cause to subside; mitigate, restrain; calm down). Sunt: (they) are (efficienda sunt is the passive periphrastic: they must be made). Efficienda is the neuter nominative plural form of efficiendus/efficienda/efficiendum (1/2), the gerundive (to be made, accomplished) of efficiō, efficere, effēcī, effectum (3, –iō): to make, complete, accomplish, bring about. Ea is the neuter nominative plural form of is/ea/id (pron.): he, she, it; this, that. (. . . so in (believed) good things must be made calmer those things. . .)
Quae is the neuter nominative plural form of quī/quae/quod (rel. pron.): who, which, that, what (ea quae = those things which, the things that). Magna is the neuter nominative plural form of magnus/magna/magnum (1/2): great, large. Et (conj.): and. Laetābilia is the neuter nominative plural form of laetābilis/laetābilis/laetābile (3): welcome, gladdening. Dūcuntur is the third person plural passive form of dūcō, dūcere, dūxī, ductum (3): to lead; think, consider, regard (as). (. . . which are regarded as great and welcome.)