I watched with some amusement an online back-and-forth debate between two family members regarding a hotly contested political issue. Both were firmly entrenched in their particular ideology and had facts to back up their claims. However, they each disputed the other’s facts, and quickly, their debate crumbled into a volley of attacks, with each using every logical fallacy imaginable to try to score points.
As I watched this relationship between two people unravel, I realized they held entirely different worldviews and were operating from two separate sets of “facts”—each disputed by the other.
I competed in speech and debate in both high school and college. I also earned a degree in Argumentation and Rhetoric and have spent considerable time studying the rules of evidence. What’s interesting to me is how, as political and social issues are adjudicated in public forums, people often allow their view of the world to be skewed and altered by arguments that wouldn’t stand a chance as legitimate evidence in a compelling, logical debate. No political “side” is immune to this problem. Take any current issue in the news, and you’ll find logical fallacies and flimsy evidence forming the backbone of multiple interpretations of reality.
This led me to take a look at some of my own views on the issues of the day. Is my thinking being swayed by unreliable, weak sources of evidence persuading me to accept their interpretation of events? Unfortunately, I think the answer is yes. There are some issues I haven’t had the time to dig into, so I tend to accept what others say about them. In some cases, I hear “facts” and just assume they’re true without really evaluating them. So, I took some time this morning to revisit the basic rules of evidence to see if I held any beliefs that were horribly misguided.
Relevance
The first principle to consider is relevance. So often in disputes, people immediately redirect the conversation by saying something like, “Well, what about…?” They bring up an unrelated event or situation to discredit the other person’s interpretation. Both parties get frustrated because they end up arguing over multiple scenarios and never resolve the original issue.
Relevant evidence should directly relate to the matter at hand. It must make a fact more or less likely than it would be without that evidence. There’s a reason courtroom motions often involve intense arguments over what’s relevant—irrelevant facts can distract, mislead, or create bias without helping resolve the real dispute.
Materiality
This is a more nuanced concept but represents a higher standard of relevance. Evidence is material if it has an actual connection to the issue and, if true, would directly impact the outcome. That’s what we mean when we say evidence “matters.”
Many poor arguments introduce evidence that doesn’t matter—ad hominem attacks, appeals to authority, irrelevant observations, or surface-level facts that don’t actually relate to the core dispute.
Strength of Evidence
Not all evidence is created equal. Some evidence carries more weight than others. People instinctively understand this—hence statements like “there’s a video,” or “a study found that…”
Here’s a quick breakdown:
- Direct Evidence: The strongest form. This includes firsthand knowledge, eyewitness testimony, and actual video footage.
- Physical or Real Evidence: Tangible objects like documents or a weapon. These are persuasive because they’re concrete and harder to dispute.
- Documentary Evidence: Written contracts or records of communication. If authenticated, these are powerful indicators of intent or fact.
- Testimony: While people can be unreliable, direct testimony from those who saw, recorded, or participated in an event is more compelling—especially when multiple testimonies corroborate each other.
- Circumstantial Evidence: Often discussed in courtroom dramas. It’s indirect but still valid when well-supported.
- Demonstrative Evidence: Diagrams, maps, or timelines. Useful for understanding, but generally considered the weakest form of direct evidence.
All of the above are types of direct evidence—the kind admissible in court. There are, of course, more nuanced legal rules (e.g., hearsay exclusions) that may not directly apply in public debate but are still relevant. On social media, hearsay runs rampant: “A friend of mine said she saw…” That’s not evidence—it’s rumor.
Sources and Expert Opinion
When facts are unclear or disputed, we often turn to experts. While expert opinion is helpful, it’s not a substitute for direct evidence.
But we do rely heavily on sources. So, what sources are considered strongest?
- Peer-Reviewed Journal Articles: These undergo expert scrutiny before publication. They follow standards of methodology, evidence, and objectivity. They’re strong sources of expert opinion.
- Systematic or Literature Reviews: These summarize findings from multiple peer-reviewed sources, using transparent methodology to identify consensus.
- Official Government Reports: While not immune to bias, many agencies produce nonpartisan, public-facing data. In the absence of better sources, these are often more reliable than private opinion pieces.
These are the strongest sources of expert opinion. Other types of sources might be considered credible, they are:
- Commissioned Case Studies / Trade Publications / Industry Reports
- Reputable News Media
These mid-tier sources can be biased or influenced by funding, editorial pressure, or access. Still, if multiple independent sources align, they’re often considered credible by the public.
The weakest sources include:
- Opinion/editorial pieces
- Blogs
- Social media posts
- Advertisements or propaganda
What amazes me is how often we allow the weakest forms of evidence—and the poorest sources—to shape our interpretation of events. We accept and share interpretations without evaluating the quality or credibility of the source.
Just my thoughts on this subject.
One thing is for sure: I won’t be sending this blog to the two relatives who were screaming at each other in that online forum. If I dared to question the basis of their interpretation of reality, I’d likely become the next target of their ire. I’ll continue to observe quietly—and try to see the humor in it all. Though, admittedly, that’s getting harder to do as we become more polarized.
