Clear Language, Clear Mind

September 13, 2011

Time travel: reading material

Filed under: Metaphysics — Tags: , , , — Emil O. W. Kirkegaard @ 17:33

I am taking a metafysics class1 and last lectur’s topic was time travel. That is an issu i sort of like but i dislike the way people discuss it, in general. Ther is a widespred lack of clarity and lack of training in the relevant logics (that is, modal logics: alethic logic and temporal logic). A fine example of that is the first essay below.

John M. E. Mctaggart – Time Is Not Real

David Lewis The Paradoxes Of Time Travel

The followup essay (2nd abov) is certainly better than the first but not quite clear enof to my taste. I do generally agree with Lewis tho. I advice people interested in the subject to lern alethic logic (S5) and read the following materials. Chapter 8.

And for those who like fiction about time travel and wants to see som fiction with time travel that seems to be non-contradictory.

Robert A. Heinlein – Time enough for love_ the lives of Lazarus Long

Robert A. Heinlein – All You Zombies


1Well, tecnically, i signed up for it but never turned up so far. I blame the timing. They put it at 0900, and even on the same day as another class (filosofical logic) altho not the same time. But it still implys that if i want to attend both lectures, then i hav to spend a lot of time on the university in one day. But i disfeel like spending that much time, unless ther is alcohol involved. :)

February 17, 2010

Necessary beings, a different counter-example

Filed under: Philosophy — Tags: , , — Emil O. W. Kirkegaard @ 22:27

“World A: Contains nothing but a single being.
World B: Contains nothing but a single being, that is a different being than the one in World A.

Do you have any objection to either of these worlds? Each seems entirely possible.

Unless you can come up with some sort of objection to THEM, we’ve got a proof. They contain nothing in common, so there cannot be any necessary being.” Smullyan-esque, source.

Where “world” means possible world. This is an interesting counter-example because it goes through even if people find the idea of an empty world contradictory/meaningless. The only part that I find disagreeable is the unnecessary (heh) “cannot” in the last sentence but I am extremely careful with modalities.

June 14, 2009

Modal logic formalization, multiple kinds of possibilities

Filed under: Uncategorized — Tags: , , , , , — Emil O. W. Kirkegaard @ 20:42

Formatting requires a PDF file.


April 23, 2009

Why something rather than nothing? An argument for the necessity of a something-world

Filed under: Philosophy — Tags: , , , , , — Emil O. W. Kirkegaard @ 20:31

PDF due to mathematical expressions that WordPress does not support.


April 17, 2009

A journey into possibility land

Filed under: Uncategorized — Tags: , , , , , , — Emil O. W. Kirkegaard @ 03:27

Intro and types

I’ve been paying very close attention as of late to a special type of discourse: Namely, about what is possible and what is impossible. This study has led me to be very careful about my language use when speaking of such things because there are multiple types of possibilities: Logical, epistemic, physical, metaphysical, practical, technological etc. I have even created a modified version of modal logic that can handle multiple types of possibilities.i Logical possibility we ought to call L-possible, epistemic possibility we ought to call E-possible etc.

Modal fallacy

And before that I discovered the modal fallacy, which occurs when people confuse the scope of the possibility used. It may be about a single proposition or an entire implication.ii

Versions: Hypothetical and absolute

And then I discovered that even a single type (and pay close attention to the words used) of possibility is used in multiple ways. Let’s call these versions. There is the absolute version and then there is the hypothetical version. I did not invest these terms; Liebniz did.iii

Since I have already written of the aforementioned let me skip them and proceed on defining absolute and hypothetical modaly. Absolute modality is the one I’ve always been talking about and hypothetical is the one that others often talk about, which confuses matters a lot, and ultimately ends up wasting a lot of time.iv


But that is not clear enough, so let me define the first. A proposition is absolutely necessary iff the negation is a contradiction (which has the form [p∧¬p]). A hypothetical impossibility is a proposition which if added to a set of propositions would result in a contradiction. This is the kind of impossibility that we’re talking about when making reductio arguments: “If something, then some contradiction, but that it impossible, so something can’t be true.” Yes, it can in the absolute sense. We ought not to confuse them.

In a later article I attacked a hypothetical impossibility for being an absolute impossibility.v

The value of the hypothetical impossibility term?

I ask now what value we have of this term. What need do we get covered by accepting this term into our collection of words? None but confusions as far as I can tell. We might as well stop called the hypothetical impossibility for an impossibility at all, and then while we’re at it, we should be very careful in our usage of the necessarily-operator when writing conditionals, so we don’t commit the modal fallacy. It doesn’t matter if we call it ‘must’, ‘cannot’ ‘has to be’ or something else. We must be very clear in our language about this matter, for if anything is certain (meant non-literally), it is that the plain English language is not at all good enough for handling modalities. Clarity is the way forward.



iiiIt is discussed here: but originally from here:



October 23, 2008

The incompatibility of omnipotence and omniscience

Filed under: Philosophy,Religion — Tags: , , — Emil O. W. Kirkegaard @ 17:56


I have recently discussed whether omnipotence and omniscience are incompatible i.e. a being cannot have both properties at the same time. Much of the discussion was centered around an argument I invented some time ago. But before we look at the argument, we need to clarify what it meant by the concepts used. The important concepts employed are omnipotence, omniscience and ‘possible’. Possible will be discussed later in the paper than the other two.

the-incompatibility-of-omnipotence-and-omniscience, PDF, 8 pages

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