That which is likely to happen; that which is most consonant to reason; for example, there is a strong probability that a man of a good moral character, and who has heretofore been remarkable for truth, will, when examined as a witness under oath, tell the truth; and, on the contrary, that a man who has been guilty of perjury, will not, under the same circumstances, tell the truth; the former will, therefore, be entitled to credit, while the latter will not.
Per Viscount Dunedin at p 767 in Re R & H Hall and W H Pim (Junior) & Co’s Arbitration  All ER Rep 763:
I do not think that 'probability' … means that the chances are all in favour of the event happening. To make a thing probable, it is enough, in my view, that there is an even chance of its happening. That is the criterion I apply…
Per Lord Reid in Davies v Taylor  AC 207, at p.213:
You can prove that a past event happened, but you cannot prove that a future event will happen and I do not think that the law is so foolish as to suppose that you can. All you can do is to evaluate the chance. Sometimes it is virtually 100 per cent: sometimes virtually nil. But often it is somewhere in between. And if it is somewhere in between I do not see much difference between a probability of 51 per cent and a probability of 49 per cent.
Per Lady Hale in Braganza v BP Shipping Ltd  UKSC 17 at para
34. … in civil cases there is only one standard of proof, viz. the balance of probabilities" (para 15). Those cases make it clear that there is not a sliding scale of probability to be applied, commensurate with the seriousness of the subject-matter or the consequences of the decision. The only question is whether something is more likely than not to have happened. Lord Hoffmann put it thus in In re B (Children) (Care Proceedings: Standard of Proof)  AC 11 at para 15:
"There is only one rule of law, namely that the occurrence of the fact in issue must be proved to have been more probable than not. Common sense, not law, requires that in deciding this question, regard should be had, to whatever extent appropriate, to inherent probabilities."
35. Some things are inherently a great deal less likely than others. The more unlikely something is, the more cogent must be the evidence required to persuade the decision-maker that it has indeed happened. As Lord Nicholls explained in In re H (Minors) (Sexual Abuse: Standard of Proof)  AC 563, at 586:
"When assessing the probabilities the court will have in mind as a factor, to whatever extent is appropriate in the particular case, that the more serious the allegation the less likely it is that the event occurred and, hence, the stronger should be the evidence before the court concludes that the allegation is established on the balance of probabilities."
Thus, for example, most parents do not sexually abuse their children. Cogent evidence is therefore required to establish that sexual abuse is more likely than not to have happened. But once it is clear that such abuse has happened, the threshold of incredulity has been surmounted, and the question of who was responsible can be answered on the balance of probabilities. Hence it is not the seriousness of the consequences of a finding of suicide which demands that there be cogent evidence to support it, but its inherent improbability.