Welcome to JustInfer

A platform for learning, teaching, and practicing formal logic.


Students can enter justifications and see if there's a corresponding inference. Given the derivation system chosen in settings, only premissible inferences are allowed. This builds good habits for students and helps students learn how their derivation system works.

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Customize Your Learning

Customize symbols and rules of inference according to your system. The symbols chosen for the connectives rewrites well-formed formulas accross all problems on this website. Additionally, you can enable features such as 'Line Check Mode' where a student must write the desired inference as well as the justification.

Go to Settings


As an instructor you can create courses, upload problems, view student progress, and set up the derivation system for your course. As a student you can solve course derivations using the JustInfer system to ensure you are doing derivations in a proper way according to your professor's chosen settings. You must create an account to gain access to these features but accounts are free and easy to create.

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