Appeal to tradition (also known as argumentum ad antiquitatem or argumentum ad antiquitam,^[1] appeal to antiquity, or appeal to common practice) is a claim in which a thesis is deemed correct on the basis of correlation with past or present tradition. The appeal takes the form of "this is right because we've always done it this way", and is a logical fallacy.^[2][3] The opposite of an appeal to tradition is an appeal to novelty, in which one claims that an idea is superior just because it is new.

An appeal to tradition essentially makes two assumptions that may not be necessarily true:

• The old way of thinking was proven correct when introduced, i.e. since the old way of thinking was prevalent, it was necessarily correct.

In reality, this may be false—the tradition might be entirely based on incorrect grounds.

• The past justifications for the tradition are still valid.

In reality, the circumstances may have changed; this assumption may also therefore have become untrue.

Appeal to tradition imports the value of not needing to reinvent ways to do things for which effective ways have already been established. But, "is fallacious when it confuses a long tradition of careful testing with the mere tendency to hold on to ideas because they are old".^[2]

An appeal to tradition can be complicated by the possibility that different people might have different views, each with their own tradition to appeal to. For example, "Augustine's appeal to tradition against the Donatists is more complicated because the Donatists had appealed to tradition against the Catholics".^[4]