What Is the Burden of Proof In a Lawsuit?
In Civil Litigation, Meaning a Lawsuit, Proof of the Allegations Is Required On a Balance of Probability Which Differs From the Criminal Standard Known As Proof Beyond a Reasonable Doubt. In a Lawsuit the Plaintiff Must Prove Both the Cause and the Loss Suffered As a Result.
A Helpful Guide to Understanding the Burden of Proof Required Within Civil Litigation Matters
Generally, within a legal proceeding, the 'burden of proof' will be borne by the side bringing the matter forward. In a litigation matter, the Plaintiff has the burden of proving that the Defendant is liable for causing losses to the Plaintiff as well as the burden of proving the amount of the losses. This is sometimes referred to as the burden of proving liability and quantum (quantum is Latin for amount).
In a criminal matter (such as charges under the Criminal Code of Canada, or quasi-criminal matter (such as charges under the Highway Traffic Act, the Crown Prosecutor bears the burden of proving the accused as guilty. However, some offences are 'reverse onus' in which the accused does have the burden of proving innocence.
Level of Proof, possibility or probability
What then is 'proof'? In civil proceedings, the burden of proof requires that the 'story' being told is demonstrated as true 'on a balance of probability' as deemed by a judge. Of course, the judge is unable to go back in time and travel to where the matter in dispute took place so as to be absolutely sure that that is said to have happened is actually what did happen. A judge can only determine 'the balance of probability' that something did happen. However, in criminal proceedings or quasi-criminal proceedings, where much more is at stake than just money, such as a person's freedom, liberty, reputation, the burden of proof is raised to the 'beyond a reasonable doubt' level which is considerably higher than the 'balance of probability' requirement in civil law matters.
Assumedly and ironically, we have all heard the expression ‘when you assume you make an ass out of you and me’.
The burden of proof requires proof of a factual theory that is on a balance of probability in that the facts are reasonably more true than false. Accordingly, the burden of proof is considerably higher than a mere possibility and requires more than guesses. Per the case of Cannito v. Madison Properties Inc., 2018 ONSC 6190, wherein various other cases were referenced, much more is needed to prove a legal csae than mere presumptions and speculations:
 In Lansdowne v. United Church of Canada (2000) BCSC 1604 the plaintiff fell on a flight of stairs in the defendant’s church. As in this case, she did not know what had caused her to fall. About a week after she fell, a friend went to the church and noticed some fraying carpet on the bottom step. The plaintiff in her action alleged that the fraying carpet was the cause of her fall. In dismissing the claim the court held the following:
 The Court cannot presume negligence on the part of an occupier of premises: Bauman v. Stein, supra, at p. 127. Nor can it presume that some act, or failure to act, on the part of the occupier caused the plaintiff to fall: Vandergaast v. Atterton  B.C.J. No. 2695 (C.A.).
 In my judgment, on the evidence before the Court here the Court would have to resort to speculation in order to find that Ms. Lansdowne's fall was caused by the loose threads on the bottom step of the stairs or some other defect in the carpeting on those stairs. This it must not do. According to Ms. Duggan, when she saw the threads one week after the accident they were coming out over the bottom step. Ms. Lansdowne, however, does not know on which step she tripped or where on the stairs she started falling. At best, both she and Ms. Lansdowne are able only to advance a theory that in some way Ms. Lansdowne's sandals got caught up in the loose threads and that as a result she tripped and fell.
 In Nandlal v. Toronto Transit Commission, 2014 ONSC 4760, (aff’d on appeal, 2015 ONCA 166), the plaintiff claimed she injured herself when she slipped on debris at the top of stairs on the defendant’s property. Although she had not seen debris when she fell, the basis for her belief she had slipped on debris was because she had seen debris in the past. On a summary judgment motion her claim was dismissed as there was no objective evidence of the slippery steps hazard, only her subjective rationalization.
 In Hamilton v. Ontario Corporation No. 2000533 o/a Toronto Community Housing Corporation, 2017 ONSC 5467 the plaintiff claimed to have slipped and fallen on the vinyl floor in the corridor outside her apartment, but gave no evidence of an alleged “hazard” at the time. Sanfilippo J. noted at para. 44-46 of the decision that an inference of causation must be based on objective facts, not speculative rationalization. In that case there were insufficient objective facts to support the plaintiff’s claim that her slip and fall was on a slippery vinyl floor outside of her apartment, notwithstanding past issues with maintenance and “detected spills” that occurred at times after her fall. Without objective evidence from which a reasonable inference of causation could be drawn, the plaintiff failed to prove on a balance of probabilities that an unsafe condition caused her slip and fall and injuries.
As was succinctly also said in Cannito within paragraph 31, "... An inference of causation must be based on objective facts rather than conjecture or speculation."
Unfortunately, all too often allegations of various kinds are based from merely a subjective viewpoint involving conjecture and speculation of the possibilities rather than via objectively considered probabilities. Accordingly, if the proof is based merely on a 'guess' that something is true, steer clear of litigation. Without directly supporting evidence, a guess is only a 'guess'. This point and concern is especially important where 'state of mind' is involved. Without powers of clairvoyance, it is impossible to know what someone else knows or thinks. What is possible may be very far from the actual truth!
Keep objective attention on the requirement that, in civil matters, the burden of proof is on the balance of 'probability'. Allegations of fact require an objectively based rationalized review of the probabilities rather than subjectively based, and often emotionally charged, speculations that amount to mere guessing. What likely happened and what might have happened are two very different perspectives.
It is often very challenging, and emotionally frustrating, for people who have suffered harms and losses to prove a case to the degree required by our legal system. Unfortunately, there is often very strong suspicion of who is likely responsible; however, there is often insufficient evidence to succeed in a legal case. In law, much more is needed than just a gut feeling.
When considering whether there is enough information available to prove a case, potential Plaintiffs struggle greatly (usually the advisor as the Plaintiffs themselves are usually oblivious to the technical legal problem) in trying to calculate a balance between when to bring a legal action and when more is required. Wait too long and Plaintiffs risks losing the right to bring legal action due to expiry of the limitation period. Sue too early and Plaintiffs risk being without enough evidence and having a case dismissed for failure to meet the burden of proof.
In civil litigation matters the party bringing the proceeding, being the Plaintiff, carries the burden of proof. The burden of proof involves both the burden of proving that the Defendant engaged in unlawful or wrongful conduct caused the harm suffered by the Plaintiff as well as providing the sum of, or value of, the loss resulting from the harm caused by the Defendant. In civil litigation, as opposed to criminal or quasi-criminal proceedings, the burden of proof is referred to as 'on the balance of probability' which means more likely than unlikely.