How to Argue that Someone Lied

Step 1. Show that person P said X.

Step 2. Show that X is false.

Step 3. Show that the best explanation for P's saying X is that P intended to deceive P's audience, e.g.,

3.1. Show that lying explains why P said X when X is false.
3.2. Show that 'P was simply mistaken about X' (because P forgot, was misinformed, etc.) is not a good explanation for why P said X when X is false.
3.3. Show that 'P is not self-deceived about X' is not a good explanation for why P said X when X is false.
3.4. As appropriate, show that other alternative explanations are not good explanations.