Obedientia est legis essentia. Obedience is the essence of the law. 11 Co. 100.

Obtemperandum est consuetudini rationabili tanquam legi. A reasonable custom is to be obeyed like law. 4 Co. 38.

Officers may not examine the judicial acts of the court.

Officia magistratus non debent esse venalia. The offices of magistrates ought not to be sold. Co. Litt. 234.

Officia judicialia non concedantur antequam vacent. Judicial offices ought not to be granted before they are vacant. 11 Co. 4.

Officit conatus si effectus sequatur. The attempt becomes of consequence, if the effect follows.

Officium nemini debet esse damnosum. An office ought to be injurious to no one.

Omissio eorum quae tacite insunt nihil operatur. The omission of those things which are silently expressed is of no consequence.

Omne actum ab intentione agentis est judicandum. Every act is to be estimated by the intention of the doer.

Omne crimen ebrietas et incendit et detegit. Drunkenness inflames and produces every crime. Co. Litt. 247.

Omne magis dignum trahit ad se minus dignum sit antiquius. Every worthier thing draws to it the less worthy, though the latter be more ancient. Co. Litt. 355.

Omne magnum exemplum habet aliquid ex iniquio, quod publica utilitate compensatur. Every great example has some portion of evil, which is compensated by its public utility. Hob. 279.

Omne majus continet in se minus. The greater contains in itself the less. Co. Litt. 43.

Omne majus minus in se complecitur. Always the greater is embraced in the minor. Jenk. Cent. 208.

Omne testamentum morte consummatum est. Every will is consummated by death. 3 Co. 29.

Omne sacramentum debet esse de certa scientia. Every oath ought to be founded on certain knowledge. 4 Co. Inst. 279.

Omnia delicta in aperto leviora sunt. All crimes committed openly are considered lighter. 8 co. 127.

Omnia praesumuntur contra spoliatorem. All things are presumed against a wrong doer.

Omnia praesumuntur legitime facta donec probetur in contrarium. All things are presumed to be done legitimately, until the contrary is proved. Co. Litt. 232.

Omnia praesumuntur rite esse acta. All things are presumed to be done in due form.

Omnia praesumuntur solemniter esse acta. All things are presumed to be done solemnly. Co. Litt. 6.

Omnia quae sunt uxoris sunt ipsius viri. All things which are of the wife, belong to the husband. Co. Litt. 112.

Omnis actio est loquela. Every action is a complaint. Co. Litt. 292.

Omnis conclusio boni et veri judicii sequitur ex bonis et veris praemissis et dictis juratorem. Every conclusion of a good and true judgment arises from good and true premises, and the sayings of jurors. Co. Litt. 226.

Omnis consensus tollit errorem. Every consent removes error. 2 Inst. 123.

Omnis definitio in jure periculosa est; parum est enim ut non subverti posset. Every devinition in law is perilous, and but a little may reverse it. Dig. 50, 17, 202.

Omnis exceptio est ipsa quoque regula. An exception is, in itself, a rule.

Omnis innovatio plus novitate perturbat quam utilitate prodest. Every innovation disturbs more by its novelty than it benefits by its utility.

Omnis interpretatio si fieri potest ita fienda est in instrumentis, ut omnes contrarietates amoveantur. The interpretation of instruments is to be made, if they will admit of it, so that all contradictions may be removed. Jenk. Cent. 96.

Omnis interpretatio vel declarat, vel extendit, vel restringit. Every interpretation either declares, extends or restrains.

Omnis regula suas patitur exceptiones. All rules of law are liable to exceptions.

Omnis privatio praesupponit habitum. Every privation presupposes former enjoyment. Co. Litt. 339.

Omnis ratihabitio retro trahitur et mandato aequiparatur. Every consent given to what has already been done, has a retrospective effect and equals a command. Co. Litt. 207.

Once a fraud, always a fraud. 13 Vin. Ab. 539.

Once a mortgage always a mortgage.

Once a recompense always a recompense. 19 Vin. Ab. 277.

One should be just before he is generous.

One may not do an act to himself.

Oportet quod certa res deducatur in judicium. A thing, to be brought to judgment, must be certain or definite. Jenk. Cent. 84.

Oportet quod certa sit res venditur. A thing, to be sold, must be certain or definite.

Optima est lex, quae minimum relinquit arbitrio judicis. That is the best system of law which confides as little as possible to the discretion of the judge. Bac. De Aug. Sci. Aph. 46.

Optimam esse legem, quae minimum relinquit arbitrio judicis; id quod certitudo ejus praestat. That law is the best which leaves the least discretion to the judge; and this is an advantage which results from certainty. Bacon, De Aug. Sc. Aph. 8.

Optimus judex, qui minimum sibi. He is the best judge who relies as little as possible on his own discretion. Bac. De Aug. Sci. Aph. 46.

Optimus interpretandi modus est sic legis interpretare ut leges legibus accordant. The best mode of interpreting laws is to make them accord. 8 Co. 169.

Optimus interpres rerum usus. Usage is the best interpreter of things. 2 Inst. 282.

Optimus legum interpres consuetudo. Custom is the best interpreter of laws. 4 Inst. 75.

Ordine placitandi servato, servatur et jus. The order of pleading being preserved, the law is preserved. Co. Litt. 363.

Origo rei inspici debet. The origin of a thing ought to be inquired into. 1 Co. 99.