A Philosophical Glossary for Beginners

Ad hoc

You call something ad hoc when it’s introduced for a particular purpose, instead of for some general, antecedently motivated reason. So, for instance, an ad hoc decision is a decision you make when there’s no general rule or precedent telling you what to do.

Philosophers sometimes accuse their opponents of making ad hoc hypotheses (or ad hoc stipulations, or ad hoc amendments to their analyses, etc.). These are hypotheses (or stipulations or amendments) adopted purely for the purpose of saving a theory from difficulty or refutation, without any independent motivation or rationale. They will usually strike the reader as artificial or “cheating.”

For instance, suppose you analyze “bird” as “any creature that can fly.” I then cite mosquitos as a counter-example. They can fly, but they aren’t birds. Now, you might fix up your analysis as follows:

A bird is any creature that can fly, and which is not a mosquito.
This would be an ad hoc response to my counter-example. Alternatively, you might fix up your analysis as follows:
A bird is any creature that can fly, and which has a backbone.
This would be an independently motivated, and more appropriate, response to my counter-example. (Of course, someone may discover counter-examples even to this revised analysis.)

Appeals to authority

In philosophy, there are no real authorities. It is never acceptable to support a position simply by pointing out that someone you’ve read holds it. You can explain why you think Philosopher X’s arguments for that position are persuasive, but a mere statement that the renowned Professor X holds a certain position carries no argumentive weight.

Ad hominem

An ad hominem argument is an argument that attacks a claim on the basis of features of the person who holds it. Two different sorts of argument are called “ad hominem arguments.” One of these is a fallacious sort of argument; the other is perfectly respectable.

The fallacious version is where you criticize someone’s views because of logically irrelevant personal defects. For instance:

His views about relationships must be false because he’s a philanderer.
His views about politics must be false because he doesn’t know what he’s talking about.

You should remember that authorities no matter how eminent can be wrong, and that scoundrels and fools–even if they are unjustified in their beliefs–might nonetheless turn out to be right. The source of a belief is one thing, and whether there are any good reasons to hold the view is something else.

The respectable argument called an “ad hominem argument” consists in objecting to someone’s claim on the grounds that it’s incompatible with other views he holds–regardless of whether you regard those other views as correct.

For instance, suppose Max says:

The U.S. Postal Service is very unreliable. I think we should allow private, for-profit companies like FedEx and UPS to compete on an equal footing with the Postal Service.
Then Sally objects:
But Max, you are a communist!
Sally is not just calling Max a . Sally’s point is that Max’s previous commitments force him to support state control and oppose private enterprise, and these commitments conflict with the view he’s advocating now. This is a perfectly legitimate criticism of Max.

Philosophers generally use the phrase “ad hominem argument” in the second sense.


In a philosophical discussion, you should call a term “ambiguous” when and only when the expression has more than one acceptable meaning.

For instance, “bank” is ambiguous (river bank, Bank of Boston).

Also, sentences can be ambiguous, as in

Flying planes can be dangerous.
Is it the activity of flying which is dangerous, or is it the planes which are dangerous?


Every child loves a clown.
Does this mean there is one lucky clown that all the children love? Or does it mean that for each child, there is a particular clown which he or she loves (but not necessarily the same clown for each child)? Or does it mean that every child is favorably disposed to clowns in general?

You should not call an expression “ambiguous” just because different people have different views or theories about it. Different people have different views about what it means to be good, but that doesn’t yet show that the expression “good” is ambiguous. It just shows that there’s some controversy over what “good” means.

Nor should you call an expression “ambiguous” just because it’s vague, or imprecise, or difficult to know what the correct philosophical theory of it is. When an argument illegitimately trades on an ambiguity, we say that the argument equivocates.


Philosophers call a term “vague” when there’s no sharp borderline between cases where the term applies and cases where it doesn’t apply.

So, for instance, it’s a vague matter how few hairs on your head makes you bald, or how many dollars in your bank account makes you rich, or how many grains of sand it takes to make a heap.

“Vague” does not mean “ambiguous.” Nor does it mean “unclear” or “difficult to understand.” Consider the following sentence:

The point of this essay is to prove that human beings never perceive material objects themselves, but only the a priori interface between a phenomenal object and its conceptual content.
This doesn’t mean anything. It’s just a bunch of words I put together in a way that doesn’t make any clear sense. You can call such prose “opaque,” or “difficult to understand,” or “gibberish.” Don’t call it “vague.”


“Philosopher Smith is equivocal here” means that he gives some argument which equivocates. It does not mean that he’s neutral or agnostic about the matter. Nor does it mean he can’t make up his mind. (These might be explanations of why he equivocates; but you shouldn’t use the phrase “He equivocates” to describe his neutrality or agnosticism or indecision.)

truth and validity

In philosophical discussions, only arguments can be valid. Not points, objections, beliefs, or claims.

Claims, beliefs, and statements are true or false.

Don’t call a claim “valid.” Don’t call an inference or an argument “true.”

falsehood and fallacy

A fallacy is an error in one’s inferences or argument. A falsehood is an error in the claims one makes.

Claims, beliefs, and statements are true or false. Only inferences and arguments can be fallacious.


Something is meaningless if it is nonsense, like “XH$%^IE”. Don’t say that a claim is meaningless if all you mean is that it is false.


In everyday speech, people often use the word “logical” like this: “John’s attitude to smoking just isn’t logical,” or: “Spock is incapable of emotion because he tries to be so logical.”

You should not speak this way in philosophical discussions. In philosophy, the word “logic” has a special technical meaning. (If you want to know what it is, you’ll have to take some courses in logic.) You should say instead:

John's attitude to smoking is unreasonable.
Also, don’t say such things as: “That was a logical point,” or “That was a logical objection,” or “This is a logical argument.”

Say instead:

That was a fair or convincing point.
That is a reasonable objection.
This is a valid or persuasive argument.

refuting and proving

Refuting a claim is showing it to be false–typically by producing reasons that make it clear that it’s false. Until you produce reasons, you may deny or reject the claim, but you won’t have refuted it.

In addition, don’t say:

Berkeley refutes Locke's claim that there are material objects.
unless you think that Berkeley has succeeded in demonstrating that Locke’s claim is false. If Berkeley has refuted Locke, then Locke must be wrong. You can’t write: “Berkeley refuted Locke’s claim, but in fact Locke was right.”

If you doubt whether Berkeley’s criticisms of Locke are successful, you should say instead:

Berkeley denies Locke's claim that...
Berkeley argues against Locke's claim that...
Berkeley rejects Locke's claim that...
Berkeley tries to refute Locke's claim that...
Similarly, you should not say that Locke has proven some claim, or shown that something is the case, unless you think that Locke’s arguments for his claim are successful. If Locke has proven a claim, then the claim must be true.

If you doubt whether Locke’s arguments for a claim are successful, then you should say instead:

Locke argues that...
Locke defends the claim that...
Locke tries to prove that...
or something of that sort.

infer and imply

Inferring is the psychological activity of drawing conclusions from premises. Only people can infer. So don’t say:

This argument infers that...
What the argument does is imply or entail a conclusion. It doesn’t infer it.

In addition to arguments implying things, sometimes we talk about people implying things. In this usage, implying is an activity, but it’s a different activity than inferring. For instance:

Sarah implied that I was a fool.
means that Sarah suggested that I was a fool, without explicitly saying so.

But in the primary usage of these words, implying is something premises and arguments do: they imply their conclusions. And inferring is something people do. People infer by looking at the evidence and deciding what hypothesis that evidence best supports.

imagine, conceive

To imagine or conceive of some possibility is to form an idea of it, to entertain that possibility in your mind. When you imagine some possibility, you are not committing yourself to the claim that that possibility actually obtains or is likely to obtain.

proposition, concept

A proposition is something that you could hold, or believe, or put forward as a claim. It’s capable of being true or false. It’s expressed in language by a complete sentence.

A concept is usually expressed in language by a noun phrase, not by a sentence.

So, we have “the concept of electricity,” and “the proposition that Socrates was a philosopher.”

thought and things

The Charles River and my idea of the Charles River are two very different things. One of them (the river) has existed since before I was born. The other (my idea of the river) has only existed since I first heard about the Charles River.

Nevertheless people often confuse thoughts with things. Don’t write like this:

Descartes realizes that even if all things are false, still he is thinking about those things, and if he is thinking about them he must exist.
You should instead say something like this:
Descartes realizes that even if all his thoughts or beliefs are false, thinking falsely is still a form of thinking, and if he is thinking at all then he must exist.

Foreign Phrases Used in Philosophy

You may come across some of these in the readings. Most of these are from Latin.


“for example”


“that is”




“compare,” “see”

a fortiori

“even more so,” or “all the more so,” as in:
If all donkeys bray incessantly, then a fortiori all young donkeys bray incessantly.

ceteris paribus

“other things being equal,” or “other things happening normally,” as in the following dialogue:
Henry: Careful! You almost dropped the vase. If you dropped it, it would shatter, and Mom would kill us.

Lola: It might not have shattered. Maybe a gust of wind would have blown the pillow off the couch just as I dropped it, and it would have landed on the pillow.

Henry: You know what I mean. If you had dropped the vase, then, if things had otherwise happened normally, the vase would have hit the ground and shattered.

de facto, de jure

de facto means “in fact,” or “as a matter of fact”; de jure means “as a matter of law.” Examples:
In this town, the clergy have de facto immunity to the traffic laws. In the eyes of the law, of course, a speeder is a speeder; but no cop hereabouts would actually give a clergyman a speeding ticket.

The old brigand wielded a de facto authority over his pack of thieves--though of course he had no legal authority.


“substitute, imitation”

ipso facto

“by that very fact,” as in:
Anyone who wears chartreuse socks is ipso facto unfit to make fashion decisions.

non sequitur

“it doesn’t follow.” The premises do not support the conclusion.


“despite what X says,” as in:
Pace Freud, it is unusual for young boys to form sexual attachments to their mothers.

per se

“itself,” as in:
It's not leisure per se which turns the mind to criminal pursuits; but rather the boredom which usually accompanies leisure.

prima facie

“at first glance,” as in:
Prima facie, it seems that George will inherit control of most of father's estate; but the will is complicated, and our lawyers are looking into it even as we speak. Perhaps they'll discover some clause that blocks George's inheritance.


“without qualification,” as in:
There are good leaders, good businessmen, and good fathers. But is there to be found anywhere in the world a man who is good simpliciter?

sui generis

“unique, one of a kind,” as in:
Greed is an appetite, like hunger and sexual desire. It's not the same thing as hunger or sexual desire, though. It's akin to them, but in other respects it's different. So there are more than just those two sorts of appetite. Greed is a sui generis appetite.