No probable cause. Nonetheless, legal professionals are used to the term, and it does indicate the reasonable foundation that is required to justify an action, even by private citizens. Terms like reasonable justification, reasonable grounds, articulable facts, etc. are more appropriately applied to private citizens, but probable cause will slip into the discussion occasionally. You establish the existence or non-existence of probable cause by showing that the facts in your case are similar to, or can be distinguished from, those of other cases where probable cause has been found or not found. Mere suspicion is not sufficient to establish probable cause.
Reasonable cause is simply a less rigorous standard than that for probable cause.
If a reasonable person would believe from the facts laid before the trier of fact that there was cause to detain, then you have reasonable cause. Rather, according to the court, a practical nontechnical probability that incriminating evidence is involved is all that is required. Neither physical proximity nor sight is essential. In the instant case the circumstances clearly suggest to any reasonable person that an offense had been committed in the presence of the security guard. Paul, with 15 years experience, observed the collection of the clothing items and concealment of two of those pieces of clothing.