Logic Model

Toy modeling of arguments with symbolically derived weights.

Setup

Install python and virtualenv, then run the setup script:

sh setup.sh

Running

# always use virtualenv to access required modules installed at setup
source env/bin/activate
# run example script below, leaving REPL open to play with
python -i model.py

Modeling Explanation

Everything is an Assertion.

A Claim is an atomic Assertion that is just text.

A Relation indicates that one Assertion either supports or refutes another Assertion.

Every Assertion has a weight, which is a derived measure of how true that Assertion is between 0 and 1, where 0 is false and 1 is true. An Assertion's weight is derived from any supporting or refuting relations. If there are none, an Assertion is assumed to be true.

# create a basic claim
c = Claim('main claim')
# add a few supporting claims
r1 = Pro(Claim('supporting claim 1'), c)
_ = Pro(Claim('supporting claim 2'), c)
# add a refuting claim
_ = Con(Claim('refuting claim 1'), c)
# print the derived weight of the original claim
print "Main Claim's Derived Weight: %s" % (c.get_weight(), )
# ==> 2/3

Now, the weird bit is that Relations are Assertions. That means Relations can support, refute, be supported by and be refuted by other Assertions.

Additionally, the algorithm to derive an Assertion's weight also takes into account the weights of the Relations themselves, lending more credence to more heavily weighted Relations.

# continuing from above...
#
# now debate over how reasonable it is to support c with "supporting claim 1"
_ = Con(Claim('refuting claim 2'), r1)
_ = Con(Claim('refuting claim 3'), r1)
_ = Pro(Claim('supporting claim 4'), r1)
# print the new derived weight of the original claim
print "Main Claim's Derived Weight: %s" % (c.get_weight(), )
# ==> 4/7

Note that the new derived weight for the main claim is lower (4/7 < 2/3) because one of the relations that supports it came under fire.