What is the difference between the tort of conspiracy and the second form of actionable conspiracy?

As Estey J. observed, the second form is structured differently. Its emphasis is on unlawful conduct rather than a predominant purpose to cause injury. In fact, a principal consequence that flows from a finding that an unlawful conduct conspiracy has been established is to exclude the availability of a “predominant legitimate motive” defence. In other words, where the elements of a conspiracy based on unlawful conduct are present, the mere advancement of the defendants’ own legitimate interests will not be a defence to liability.[54] The key difference in the two forms of the tort is made clear in Salmond on Torts:[55] A second form of actionable conspiracy exists when two or more combine to injure a third person by unlawful means – e.g. the commission of a crime or tort, or the infringement of a guaranteed constitutional right.... In such a case it is irrelevant that the object of the conspirators in using those means may be legitimate. Combinations of this kind must be contrasted with what might be called "Quinn v. Leatham conspiracies," where the means are legitimate but the object is not…. Hence a conspiracy may be actionable if either the end or the means, or both, are unlawful.[56]