What is probable cause and what is the test?

" 'Probable cause exists when the facts known to the arresting officer would persuade someone of "reasonable caution" that the person to be arrested has committed a crime. [Citation.] "[P]robable cause is a fluid conceptturning on the assessment of probabilities in particular factual contexts . . . ." [Citation.] It is incapable of precise definition. [Citation.] " 'The substance of all the definitions of probable cause is a reasonable ground for belief of guilt,' " and that belief must be "particularized with respect to the person to be . . . seized." ' " (People v. Scott (2011) 52 Cal.4th 452, 474.)