Occam’s Razor is, to me, one of the most ingenious tools of critical thinking. It is not a mechanism that automatically produces truth. But it forces us to make the cost of our assumptions visible.
The basic idea is often expressed roughly as follows: if several explanations are compatible with the known facts, we should not introduce additional assumptions without good reason. The simplest explanation is therefore not automatically true. But every additional assumption increases the burden of proof.
The more unsupported additional assumptions an explanation requires, the greater its burden of proof.
Where does Occam’s Razor come from?
The name refers to William of Ockham, an English Franciscan friar, theologian, philosopher and major logician of the late Middle Ages. He lived approximately from 1287 to 1347 and was one of the influential thinkers of scholastic philosophy.
Ockham was not a modern philosopher of science in today’s sense. He worked in a world of theological and metaphysical debate. Yet within that world he developed an intellectual attitude that still feels strikingly modern: when explaining something, one should not introduce more assumptions than are genuinely needed.
The famous Latin formula “Entia non sunt multiplicanda praeter necessitatem” — “Entities should not be multiplied beyond necessity” — is often attributed to Ockham. Historically, caution is appropriate: the exact wording probably does not come directly from him. It nevertheless captures a way of thinking that fits his work very well.
Ockham’s basic idea: no unnecessary entities or auxiliary constructions
Medieval thought often explained phenomena by introducing additional metaphysical entities, hidden forms or abstract intermediate agencies. Ockham was sceptical of such duplication. If an explanation works without an extra entity, we should not assume that entity merely because it sounds philosophically elegant.
This does not mean:
“The world is always simple.”
It means instead:
“Do not invent an additional level of explanation unless you need it.”
Nominalism and parsimony
Ockham is often associated with nominalism. Put very simply, he was sceptical of the idea that general concepts such as “humanity”, “redness” or “animality” must exist as independent things outside individual human beings, red objects or animals.
Here again we see the same impulse: we should not populate the world with additional entities if individual things and our concepts already suffice to explain what we are talking about.
Why this medieval idea remains so powerful today
For me, the connection to fake news and conspiracy theories is obvious. Many such narratives begin with a seemingly small additional assumption:
- “Perhaps this photograph was faked.”
- “Perhaps this authority is lying.”
- “Perhaps there is a secret plan.”
But once counterarguments appear, further assumptions become necessary: then other photographs must also be fake, other authorities must be involved, scientists must have been bought, the media must be controlled and witnesses must have been silenced.
A small suspicion grows into an ever larger structure of additional assumptions. At precisely this point, Ockham’s old philosophical idea becomes a highly modern tool.
What does it “cost” me to believe a claim?
I find it especially useful to ask about the cost of a claim. I do not mean financial cost. I mean the intellectual price I have to pay in order for the claim to work.
For example, I can ask:
- How many additional assumptions do I have to accept?
- How many observations do I have to reinterpret?
- How many independent measurements do I have to dismiss as false or fabricated?
- How many people would have to deceive others or remain silent over long periods?
- How many institutions would have to coordinate their actions?
- How many new auxiliary hypotheses do I need whenever an objection arises?
An explanation becomes more “expensive” when it constantly requires new assumptions. This is exactly where Occam’s Razor becomes especially useful.
Example: what does belief in a flat Earth cost?
Consider the claim that the Earth is flat. At first, this may sound like merely an alternative geometrical picture. In reality, the price is enormous. Anyone who wants to maintain the claim must accept numerous additional assumptions.
Among other things, one would have to explain why:
- ships and distant objects disappear behind the horizon,
- the visible night sky changes with geographical latitude,
- time zones and solar positions work consistently around the world,
- a round Earth shadow is observed during lunar eclipses,
- satellite communication, navigation and weather observation work,
- people in very different countries measure the same approximately spherical shape,
- air and sea routes can be calculated successfully using a spherical Earth model.
To save the flat-Earth idea, one would therefore have to do far more than assume a different shape of the Earth. One would also have to reinterpret many independent observations and often assume that scientists, space agencies, surveyors, pilots, sailors, telecommunications companies and countless other actors are either mistaken or participating in a coordinated deception.
That is a very expensive explanation. The assumption of an approximately spherical Earth explains the same observations with far fewer additional assumptions.
Example: what does the claim that humans never landed on the Moon cost?
The same applies to the claim that the crewed Moon landings never happened. Here, too, one assumption is not enough: “The footage was made in a studio.”
For the conspiracy narrative to work, one would additionally have to assume that:
- a large number of people involved remained silent over decades,
- technical data and mission documentation were systematically fabricated,
- independent observers and rival states were deceived or cooperated,
- later measurements and observations were manipulated to fit the story,
- no robust internal evidence of the alleged fraud emerged over many decades.
The conspiracy claim begins with a seemingly simple statement but creates a constantly growing apparatus of auxiliary hypotheses. Every new objection leads not to abandoning the theory, but to adding another assumption:
“Then even more people must have been involved.”
“Then that measurement was faked as well.”
“Then that institution is also part of the conspiracy.”
This is precisely where Occam’s Razor becomes especially sharp: a theory that immunizes itself against every possible objection by adding new unsupported assumptions explains less and less while claiming more and more.
A cost matrix for claims
For practical evaluation of a news item or conspiracy narrative, we can use a small mental cost matrix:
Occam’s Razor does not automatically decide what is true
One limitation is essential: Occam’s Razor proves nothing. Reality is allowed to be complicated. A complicated explanation may be true and a simple one false.
We must therefore not turn the principle into the fallacy:
“This explanation is simpler, therefore it must be true.”
Occam’s Razor does not automatically decide which explanation is true. Rather, it helps us identify unnecessary additional assumptions and keep the burden of proof where extra claims are introduced.
The self-sealing theory
Many conspiracy theories have a remarkable property: counter-evidence is not perceived as a problem, but as confirmation.
- There is no evidence? Then the conspiracy is exceptionally well hidden.
- Scientists disagree? Then they have been bought.
- The media do not report it? Then they are censoring it.
- The media do report it? Then they are trying to manipulate the public.
Such a theory is sealed off from every possible experience. It can practically no longer lose. But precisely for that reason it also gains no explanatory power.
Occam’s Razor asks:
How many additional assumptions were introduced solely to protect the theory from failure?
A practical checklist against fake news
Before I believe or share a spectacular claim, I can ask myself:
- What exactly is being claimed?
- Which assumptions are genuinely necessary?
- Which assumptions were added only to fend off objections?
- Is there a simpler explanation that accounts for the same observations?
- What independent evidence exists?
- What else would I have to believe for the claim to be true?
- How high are these “costs”?
- What could, in principle, falsify the claim?
The last question is especially important. Anyone who cannot name a possible answer to the question “What would convince you that you are wrong?” may no longer be defending a testable hypothesis, but a belief.
Another problem: asymmetric scepticism
Fake news and conspiracy theories often reveal a peculiar asymmetry. Perfect evidence is demanded for the established explanation. For the alternative explanation, by contrast, a suspicion, a YouTube video, an unclear photograph or the phrase “That cannot be a coincidence” is considered sufficient.
Occam’s Razor helps here as well. It reminds us that not only the established explanation must be tested. The competing hypothesis also has costs and also requires evidence.
My conclusion
For me, Occam’s Razor is therefore an ingenious tool of critical thinking. It does not force us always to choose the most convenient or popular explanation. Rather, it forces us to make the price of our assumptions visible.
The decisive question is:
What does it cost me in additional assumptions if I believe this claim?
For many forms of fake news and many conspiracy theories, that price is astonishingly high.