Imagine that John complains to Peter that he did not sleep well last night. He then says that he will attempt to sleep weller the next time. This sentence fails.

Imagine that John complains to Peter that he did not sleep good last night. He then says that he will attempt to sleep gooder the next time. This sentence also fails.

Where is my simplified English language? I have to do a project about it later.

The prima facie principle is a principle that deals with justified belief in cases where opposing evidence is absent. The principle can be stated as this:

P. If one has prima facie evidence for P and lacks evidence for not-P at time t, then one is justified in believing P at time t.

Prima facie evidence is such evidence that in absence of other evidence that evidence is enough to establish a justified belief. Suppose we grant (P), then the question of which evidence is prima facie evidence arises. But a more interesting question is what conditions must prima facie evidence satisfy? I think we ought to define evidence first.

Evidence is a somewhat vague term. Evidence for what exactly? Many dictionaries define evidence as something that makes another thing more likely to be true. So, evidence is relative to a proposition. In Bayesian terms, we can define evidence as:

P(o|e) > P(o)

Evidence is whatever makes some proposition, o, more likely than without taking the evidence into account. When are we justified in believing some proposition? Maybe it is when the probability that it is true is larger to some degree than the probability that it is false.1 Suppose that to be justified in believing a proposition, the probability of that proposition must be at least 0.55 given the available evidence. In that case, prima facie evidence is any evidence that makes the probability of a proposition become 0.55 or greater.

We cannot say that it is evidence with a magnitude of 1.5, because that way we wound assume that the prior probability is always 0.5, but we cannot assume that. The evidential strength of prima facie evidence is, therefore, relative to the prior probability of the proposition.


There are some interesting areas where prima facie evidence is used. One example could be an attempt to justify empiricism as a method of inquiry (broadly speaking). An argumentation could go as this: Empiricism seems to be true, therefore, in absence of any counter evidence (i.e. evidence for the negation) then we are justified in believing empiricism.

The key word is ‘seems’. The idea is that what something seems to be, is prima facie evidence for that it is what it seems to be. Our initial impression of something is based on intuition (among other things), so intuition is a source of prima facie evidence. But how do we know that? Experience has taught us, but then we are begging the question in our justification of empiricism; we assumed that experience is reliable to justified that experience is reliable.

Another application could be an argument for the existence of god. The argument is that, many people know god (or think they know god) and that is prima facie evidence of god. If we suppose that all atheistic evidence has been rebutted, then one is justified in believing in god.

1I suggested this before, see “Et lidt længere forsvar af evidentialisme”

Also brought on here.


This article will focus on an evidentialist approach to knowledge. An evidentialist states the individually necessary and jointly sufficient conditions for knowledge as:

1. S believes P.

2. P is true.

3. S’s belief that P is justified.

However, this view was proven to be inadequate because that there is at least one situation where all the conditions are met but the belief does not qualify as knowledge.1 I will paraphrase the first of the two Gettier examples used in the original paper here.

“Suppose that Smith and Jones have applied for a certain job. And suppose that Smith has strong evidence for the following conjunctive proposition:

d. Jones is the man who will get the job, and Jones has ten coins in his pocket.

From (d) Smith concludes (e)

e. The man who will get the job has ten coins in his pocket.

Now, Smith has justification for believing that (e). But imagine, further, that unknown to Smith, he himself, not Jones, will get the job. And, also, unknown to Smith, he himself has ten coins in his pocket. Proposition (e) is then true, though proposition (d), from which Smith inferred (e), is false.”2

So, Smith’s belief is true, but only as a matter of epistemic luck. Such cases are called Gettier cases. To many people the above situation is not a case of knowledge, I will grant that for now and discuss possible solutions. Perhaps JTB is missing at least one more condition for the description to fit what we normally mean by knowledge, such a condition set with one or more conditions is called JTB+.

However, it could also be that one of the conditions in JTB could be improved. Let’s focus on the first.

A proposal for a forth condition is:

4. S’s belief that P is not inferred from any falsehood.3

Is (4) successful? Unfortunately not. The problem is that one’s justification can be an true but still problematic thing. SEP writes that:

“Suppose, for example, that James, who is relaxing on a bench in a park, observes a dog that, about 8 yards away from him, is chewing on a bone. So he believes

5. There is a dog over there.

Suppose further that what he takes to be a dog is actually a robot dog so perfect that, by vision alone, it could not be distinguished from an actual dog. James does not know that such robot dogs exist. But in fact a Japanese toy manufacturer has recently developed them, and what James sees is a prototype that is used for testing the public’s response. Given these assumptions, (5) is of course false. But suppose further that just a few feet away from the robot dog, there is a real dog. Sitting behind a bush, he is concealed from James’s view. Given this further assumption, James’s belief is true. So once again, what we have before us is a justified true belief that doesn’t qualify as an instance of knowledge. Arguably, this belief is directly justified by a visual experience; it is not inferred from any falsehood. But if (5) is indeed a non-inferential belief, then the JTB account, even if supplemented with (iv), gives us the wrong result that James knows (5).”4

As explained above it was inferred by an experience and those can, arguably, not be false. But still there is something wrong with his visual experience, and that is that it reports a falsehood. Maybe (4) can be changed to catch that:

4′. S’s belief that P is not inferred from any falsehood or malfunctioning experience.

Where ‘malfunctioning experience’ is taken to mean an experience from which one can infer a wrong belief. Yet this condition may give us the opposite problem: that there is knowledge which the JTB+ says is not knowledge. A such case would be any case where we justify a belief from an experience that could be used infer a falsehood. I cannot think of any, but maybe further pondering will reveal an example.

Alternatively, we could dismiss the approach to knowledge. The approach I have in mind is: We have some non-conscious understanding or definition of knowledge. We can identify this understanding or definition through an analysis and set forward a set of conditions for something to be knowledge.

But I cannot help but wonder, why do we not dismiss the intuitive understanding of knowledge? We could just define what we mean by the term knowledge and by done with it. After all, meanings of terms shift in time, so, probably, after some time, the new definition will seem intuitive to us.

Another reason for dismissing it, is that we also take that approach in physics. We all have an intuitively understanding of what time is, but this understanding proved to be false by relativistic physics.

1L. Gettier, Edmund “Is Justified True Belief Knowledge?”, Analysis 23 ( 1963): 121-123.

2I did not include everything that was originally written, see Ibid.

3Quoting Stanford Encyclopedia of Philosophy, “See, for example, Armstrong 1973, p. 152, and Clark 1963. For further references, see Shope 1983, p. 24. This monograph provides a comprehensive discussion of the Gettier literature up to 1980. For a shorter but excellent discussion of the Gettier problem, see the Appendix in Pollock 1986.”