TOAST The Online Argument Structures Tool
from ARG-tech

TOAST (The Online Argument Structures Tool) is a web-based implementation of the ASPIC+ framework, characterised by Prakken [2010]. Currently, it works only with a simple propositional logic and simple formulae in the knowledge base (i.e. logical conectives aren't currently parsed). The system is a work-in-progress, however, so new features will be added before long.

There are two interfaces to TOAST - a web form and a web service. The web form allows you to enter an argumentation system, view the results of evaluating it. The web service interface allows you to connect your own applications to TOAST and recieve the results in JSON format. Documentation for the web service is available.

The syntax for using the TOAST web interface is as follows:

Knowledge base

The knowledge base is split into Axioms, Premises and Assumptions. For all three sets, formulae are entered as a semi-colon seperated list of terms, with "~" being used for classical negation e.g. p; q; something_in_prose; ~r;

Note that formulae cannot contains spaces.

Knowledge base preferences

The knowledge base prefereces are entered as a semi-colon seperated list of elements, with each element having the following format:

lessPreferredFormula < morePreferredFormula;

Note that as per the ASPIC+ theory, axioms cannot be part of a preference relation.


Rules are entered in the following format:

[label] {comma-seperated list of antecedents}{implication}{consequent};

Note: there must be a space between tthe label and the start of the rule, but NOT between either the antecedents and the implication, nor the implication and the consequent.

Antecedents and consequents are wffs in the language being used. Implication is either "=>" (for a defeasible rule) or "->" for a strict rule.

For instance:

[r1] p,q->r; (a strict rule for r, with antecedents p and q, with label r1)
[r2] s=>~t; (a defeasible rule for ~t, with antecedent s, with label r2)

All rules MUST be labelled. Using a rule's label allows it to be undercut, by expressing another rule with the negate of the rule's label as its consequent, thus:

[r3]u =>~[r1]; (a defeasible rule where u undercuts the rule r1)

General rules are currently NOT supported, but including this is a high priority.

Rule preferences

Rule preferences are entered as a semi-colon seperated list of elements, with each element having the following format:

[label_of_less_preferred_rule] < [label_of_more_preferred_rule]


[r1] < [r2]

Note that as per the ASPIC+ theory, strict rules cannot be part of a preference relation.


Contrariness relations allow one formula to be declared the contrary of another, or for two formulae to be declared contradictory.

TOAST accepts both these these forms. Examples will be used to describe the syntax:


This means that p is a contrary of q.


This means that r and s are contradictory, and is the same as:



The query determines whether or not there is an acceptable argument for the given formula, under the specified semantics, in the abstract framework derived from the given AS.

Last link/weakest link

This decides whether the last link or weakest link principle is used to determine the ordering on arguments. Please refer to [Prakken 2010] for details.


H. Prakken. An abstract framework for argumentation using structured arguments. Argument and Computation, 1(2):93-124, 2010.