Doctrines of inchoate speech crimes conventionally require that there be a likelihood that the speech act in question cause subsequent lawless action. Our provision requires that the incitement be conducted in a manner so as to “significantly” increase the likelihood of the commission of the crimes. This filter excludes petty “barstool” criminal advocacy which have no realistic possibility of prompting anyone to commit grave crimes. Here it is worth recalling that the ICC’s Statute claims jurisdiction over only “the most serious crimes of concern to the international community as a whole” and is complementary to national criminal jurisdictions.

Adjudicating speech crimes in a preventative manner presupposes an assessment that a speech significantly elevates the risk that an international crime will occur. Such predictive reasoning based on probability is inherently speculative and is often determined by prosecutors and judges on the basis of hunches and personal opinion, and this is why international tribunal judgments are often characterized by misleading metaphors that compare inciting speech acts to fire and conflagration, poison, viruses or to the “marketplace of ideas.”

We recommend a more rigorous risk framework to determine the likelihood that a speech act could cause an offence that is based on peer-reviewed social science. Recent social research has identified many of the key factors in mass persuasion. Distilling the social science findings, we can provide a checklist of 11 factors that are known to elevate the risk of violence, including:

1. The speaker occupies an official position of authority.
2. The speaker is perceived as credible by his/her audience.
3. The speaker is perceived as charismatic by his/her audience.
4. The speaker is adept at summoning up pre-existing cultural symbols and narratives to cultivate historical grievances. 
5. The speaker makes dehumanizing references, refers to past atrocities and calls for revenge against the out-group.
6. The speaker uses intense language replete with vivid images, graphic metaphors and exaggerations.
7. His or her speech is experienced as “powerful” by an audience.
8. The message of the speaker is repeated across a variety of mass communication formats, from radio to television to Twitter.
9. The speaker wields a monopoly on the means of communication or can censor and suppress information. 
10. The emotional state of the audience is affected by wider circumstances of insecurity and uncertainty.
11. His or her speech arouses fear by labelling a direct threat and then identifying a distinct and foreseeably violent course of action that can be taken by the audience to remove the source of that threat.

This list is not exhaustive, and additional elements may be added as knowledge improves. In themselves, none of these variables are causal in the conditio sine qua non sense, nor do they always denote uptake on the part of the audience. Social science research alone cannot determine a trial chamber verdict: each individual case will be decided on the prevailing international criminal law, the specific evidential fact pattern and the merits of the arguments of the parties. Nonetheless, identifying the leading conditions most likely to persuade an audience can assist pre-trial and trial chamber judges in assessing the likelihood that international crimes against protected groups will ensue.

Constructing a multi-factorial matrix out of the list above could guide prosecutors as they discharge their due diligence obligations under international law and assess the likelihood that an utterance by a politician or prominent public figure will have grave consequences. The matrix could be quantified, with each factor above given a rating from 1-10 based upon a qualitative evaluation of each element in the matrix. Prosecutors are advised to determine prior to any review the statistical threshold (e.g., 80%) required to merit an indictment.

International criminal tribunals need to return to the approach to incitement developed at Nuremberg that held Julius Streicher liable as an accomplice to wider crimes planned and perpetrated by the Nazi High Command, based upon his patently genocidal speech acts. We strongly advise prosecutors to consider indicting on the basis of inchoate crimes such as incitement to genocide and forms of liability for completed crimes such as complicity that do not require a high level of direct causation. By charging populist demagogues such as Vojislav Šešelj (ICTY) under theories of direct causation such as instigating, prosecutors are compelled to advocate an inaccurate account of the consequences of speech, and they are also less likely to persuade the court and secure a conviction. In most criminal law settings, it is better to be on the more secure ground of inchoate crimes and complicity, and to defend a moderate position effectively and successfully, rather than to grasp for a level of causation and responsibility that is out of reach.