Truth Tables

The TruthTable class indicates that a code block will contain truth table exercises.

Simple Truth Tables

You can create simple truth table problems, checking to see if a formula is a tautology, by also adding the class Simple, like so:

~~~{.TruthTable .Simple}
2.1 ((P/\Q)\/R)<->((P\/R)/\(Q\/R))
~~~

the number 2.1 indicates the exercise number, and the formula is the one for which you will be constructing a truth table. This produces:

2.1

You can also use a comma-separated list of formulas, like so:

~~~{.TruthTable .Simple}
2.2 (P/\Q)\/R, (P\/R)/\(Q\/R)
~~~

This example produces:

2.2

Simple truth tables can be (by default) checked for correctness, and will be considered correct when every row is filled in correctly. A problem can also be solved by indicating a counterexample to tautology. A row is considered a counterexample if all the formulas in the problem are false on that row.

Validity Truth Tables

If, instead of Simple, you add the class Validity, like so:

~~~{.TruthTable .Validity}
2.3 P :|-: ((P/\Q)\/R)<->((P\/R)/\(Q\/R))
~~~

the result is a truth-table for checking the validity of an argument (in this case, P :|-: ((P/\Q)\/R)<->((P\/R)/\(Q\/R)), where :|-: is just a stylized way of typing out the turnstile). The above produces:

2.3

Validity truth-table problems can include comma-separated lists of formulas to both the left and right of the turnstile. For example,

2.4

produces:

~~~{.TruthTable .Validity}
2.4 P,Q :|-: (P/\Q), (P\/R)/\(Q\/R)
~~~

Validity truth tables can be (by default) checked for correctness. A table is correct when every row has been filled in, with rows that are counterexamples to validity marked F, and rows that are not counterexamples to validity marked T. A counterexample to validity can also be provided directly by pressing the counterexample button and entering the truth values of the relevant row. A row is considered a counterexample to validity only if all the formulas to the left of the sequent are true, and all the formulas to the right of the sequent are false.1

Partial Truth Tables

You can also create truth table problems that involve filling in a single row. To do this, add the class Partial, like so:

~~~{.TruthTable .Partial}
2.5 (P/\Q), (P\/R)/\(Q\/R)
~~~

creating something like this:

2.5

By default, the row is considered correct if it is filled in correctly, with any assignment of truth values to the atoms. However by using givens (see below), partial truth tables can be used to ask students to test for variety of different properties.

Advanced Usage

Options

In addition to setting a custom point value or turning off submission by adding points=VALUE and submission="none", several other options are available for truth tables:

Name Effect
nocheck Disables the "check" button
nocounterexample Disables the "counterexample" button
exam Allows for submission of work which is incomplete or incorrect
autoAtoms Prepopulates atomic sentence columns with truth values
turnstilemark Uses and rather than T and F under the turnstile
immutable Makes the truth table immutable (useful for displaying truth tables)
strictGivens Makes givens (see below) immutable
hiddenGivens Hides givens (see below)

So for example,

~~~{.TruthTable .Validity options="nocheck nocounterexample"}
2.6 P :|-: Q
~~~

Generates:

2.6

Counterexamples

There are also a number of options that affect what counts as a counterexample. these are set using the counterexample-to attribute. The options are:

Name Counterexample is
validity a situation in which all formulas are false
tautology Same as validity
equivalence a situation in which two formulas have different truth values
inconsistency a situation in which all formulas are true

In the case of simple truth tables, these apply to all formulas. In the case of validity truth tables, a counterexample is a situation in which the formulas to the left of the turnstile are all true, and the ones to the right of the turnstile have the counterexample property. Hence, a validity problem in which the counterexample is equivalence is basically using a truth table to test whether the formulas to the right of the turnstile are equivalent "under the assumption" that the formulas to the left of the turnstile are true.

Systems

The way that formulas are parsed and displayed can also be customized. This is done by setting the system attribute to indicate which formal system you are drawing your syntax from. So for example,

~~~{.TruthTable .Simple system="LogicBookSD"}
2.7 A > B & C
~~~

will generate:

2.7

The available systems are: prop montagueSC LogicBookSD LogicBookSDPlus hausmanSL howardSnyderSL ichikawaJenkinsSL hausmanSL magnusSL magnusSLPlus thomasBolducAndZachTFL tomassiPL and hardegreeSL.

Givens

It is also possible to give a "partial solution" to a truth table problem, in which the truth table is partly filled in, and the student needs either to complete it or correct it. To pre-populate simple and validity tables with "givens" in this way, write the truth table you want, preceded by the bar character |, after the problem. So,

~~~{.TruthTable .Simple}
2.8 P \/~P
|   T - FT
|   F - TF
~~~

Generates

2.9
T - FT F - TF

You do need to fill in every row entirely. If a row is the wrong length, or if there are the wrong number of rows, the table will not be pre-populated. If you wish to make the givens you assign immutable (to clarify that they are a hint, rather than something that needs to be corrected), you can use the strictGivens option.

Givens behave similarly for partial truth tables. For example,

~~~{.TruthTable .Partial}
2.10 P \/~P
|   F - TF
~~~

will produce:

2.10
F - TF

However: if a partial truth table is constructed with givens, then a solution will only be accepted if it is "consistent" with the givens. So in the above case, the only acceptable solution will be one that assigns T to P. The givens can be hidden, using hiddenGivens if you want to, for example, ask students to make a sentence truth and you want them to figure out the relation between the truth of a sentence and the truth value of the main connective.

if you wish to hide some givens, but not others, you can use a colon to separate the sentences that will have visible truth values from those that will not. For example, you can write

~~~{.TruthTable .Partial options="hiddenGivens"}
2.11 Q : Q->P
|    T   TT -
~~~

to create a problem in which the student must make Q->P true under the assumption that Q is true. The result is like this:

2.11
T TT -

so this can also be used to create problems in which students are responsible for filling in a certain row of the truth table.

Finally, if more than one row of givens is provided to a partial truth table, then any solution which is compatible with any one of the rows will be accepted. So for example, you can write:

~~~{.TruthTable .Partial options="hiddenGivens"}
2.12 P/\Q, P\/Q
|    -T -  -F - 
|    -F -  -T - 
~~~

In order to ask students to provide a row that witnesses the inequivalence of these two sentences. The result will be:

2.12
-T - -F - -F - -T -

  1. There's some arbitrariness in how we choose to think about the validity of multi-conclusion arguments. This approach is the most natural from the point of view of the sequent calculus.