Category: Logica Docens

A Point of Logic

Jouni Lappi, having read the Substack article on Heidegger and Carnap, writes:

One thing I cannot get my head around is this part:
’Nothing is F’ => ’Everything is not F’
Maybe there is some syntactic agreement behind the ’Everything is not F’, that I do not understand. In my layman ears it sounds strange and wrong. I would understand ’it is true for every thing, that it is not F’. Say in my universe there is A, B and F.
’Nothing is F’ is false, ’Everything is not F’ is true.
This is probably some newbie error in thinking. And especially because of that,  I would appreciate if you could explain this to me and point out where I think wrong.
First of all, what you express as a conditional is really a biconditional. Thus
1) Nothing is F <=> Everything is not F. 
Bear in mind that ‘F’ is a predicate. If it names anything, it names a property, not an individual. (Properties, by definition, are instantiable items; individuals are not.)  So an instance of (1) is 
2)  Nothing is fragile if and only if everything is not fragile.  
Surely (2) is true; indeed it is necessarily true.  In a universe U in which there are exactly two individuals, a and b, and one property F-ness, if neither a nor b instantiates F-ness, then every/each  individual in U does not instantiate F-ness, and vice versa. 
Are you perhaps  confusing individuals and properties?  Or perhaps you do not appreciate that ‘everything’ is being used above as a distributive, not a collective term? ‘Everything’ means each thing; it does not mean the collection of things.  

Russell’s Paradox Explained

Reader Requests Advice re: Learning Basics of Philosophical Argumentation

A New Zealand reader writes,
 
I was hoping if you are able to provide me with some guidance regarding where to begin learning the basics of philosophical arguments. I’ve been trying to understand how to evaluate political and theological debates for awhile, but despite my interest I often find them go away over my head. I found your Substack a couple of weeks ago and was delighted to find your articles not only quite easy to follow but made plenty of sense. So I thought why not give it a try and ask you for help in getting better critical thinking. It would be wonderful if you are able to help with this.
 
Many thanks,
Cameron
 
I am happy to be of assistance, Cameron. Jay F. Rosenberg's The Practice of Philosophy: A Handbook for Beginners comes to mind.
 
Your question has been put to me before. Here is a post from 2011 in which I make a few other suggestions. You will also find the comment thread to that post useful.
 
If anyone wants to help Cameron in his quest, comments are enabled below.
 

The Difference between Posing and Begging a Question

I found the nifty graphic below over at Flood's place.  It is a pithy and pictorial presentation of a point I have been hammering away at online for the last twenty years. Here is a Substack hammer-job. Some say we should give up the fight and let the forces of linguistic decadence obliterate the distinction between posing and begging a question. I am inclined to say that we should fight on against the anti-civilizational forces while well aware that fighting-on may be nothing more than a pointless rear-guard action.

What say you?

Begs the Question

 

The Ersatz Eternity of the Past: Denied by Lukasiewicz!

The Pole denies the actuality of the past and in consequence thereof the ersatz eternity or accidental necessity (necessitas per accidens) of the past.

Quasi-literary Preamble:

What has been, though it needn't have been, always will have been.  What time has mothered, no future time can destroy.   What you were and that you were stand forever inscribed in the roster of being whether or not anyone  ever reads the record.  What you have done, good or bad, and what you have left undone, good or bad, cannot be erased by the passage of time. You will die, but your having lived will never die. This is so even if you and your works and days are utterly forgotten. An actual past buried in oblivion remains an actual past. The erasure of memories and memorials is not the erasure of their quondam objects. The being of what was does not depend on their being-known; it does not rest on the spotty memories, flickering and fallible, of fragile mortals or their transient monuments or recording devices.

But how paltry the ersatz eternity of time's progeny!  Time has made you and will unmake you.  In compensation, she allows your having been to rise above the reach of the flux.  Thanks a lot, bitch!  You are one mater dolorosa whose consolation is as petty as your penance is hard.

………………………….

I posted a precursor of the above on 10 March 2010.  It elicited an astute comment from Alan Rhoda.  He wrote:

You here express the tense-logical idea that p –>FPp, that if something is the case, then it will thereafter always be the case that it has been the case. In Latin, facta infecta fieri non possunt. [The done cannot be undone.]

Believe it not, this has been denied by the famous Polish logician Lukasiewicz, no less. He seems to have accepted a version of presentism according to which (1) all (contingent) truths depend for their truth on what presently exists, and (2) what presently exists need not include anything that suffices to pick out a unique prior sequence of events as "the" actual past. Accordingly, truths about the past may cease to be true as the passage of time obliterates the traces of past events. Lukasiewicz apparently found this a comforting thought:

"There are hard moments of suffering and still harder ones of guilt in everyone’s life. We should be glad to be able to erase them not only from our memory but also from existence. We may believe that when all the effects of those fateful moments are exhausted, even should that happen only after our death, then their causes too will be effaced from the world of actuality and pass into the realm of possibility. Time calms our cares and brings us forgiveness." (Jan Lukasiewicz, "On Determinism" in  Selected Works, ed. L. Borkowski, North-Holland, Amsterdam, 1970, p.128.)

Lukasiewicz JanThat is  to my mind an amazing passage from Lukasiewicz both because of his rejection of the tense-logical principle, p –>FPp,  and because of the consolation he derives from its rejection.

I myself find it very hard to believe that there wasn't an actual unique past. I find it impossible to believe that, with the passage of enough time, past events will somehow go from being actual to being merely possible. It seems obvious to me, a plain datum, that there is an important difference between a past event such as Kierkegaard's engagement to Regine Olsen, which actually occurred, and a merely possible (past) event such as his marriage to her which did not occur, but could have  occurred, where 'could have' is to be taken ontically and not epistemically. Now that datum tells against presentism — unless you bring God into the picture which is what Rhoda does.  For if the present alone exists, then the wholly past does not exist, which implies that there is no difference between a merely possible past event and an actual past event.

Alan Rhoda responds:

Yes, in my paper "Presentism, Truthmakers, and God" (Pacific Philosophical Quarterly 2009). I argue that the best way for presentists to supply truthmakers for truths about the past is to appeal to divine memories.

I accept the datanic nature of your distinction between the actual and the merely possible past. I'm not clear, however, on why that distinction by itself should count against presentism. Unlike Lukasiewicz, most presentists do posit present grounds for that distinction. The live question is what sort of present facts, if any, could serve the presentist's purposes. That's where my argument for theistic presentism gets its purchase.

If only that which exists now, exists, then that which existed does not exist. If to exist = to be actual, then that which existed is not actual. Since what existed is presumably not impossible, that which existed is merely possible. It therefore looks as if one can get very quickly from the distinction I pointed out to a rejection of atheistic presentism. Atheistic presentism cannot supply the truth-makers for past-tensed truths such as 'Kierkegaard was engaged to Regine Olsen.'

Atheistic presentists need to find present facts to ground the distinction in question.  Now there are some present facts that could serve to ground some past-tensed truths. Consider 'Bill Sykes the burglar entered my house yesterday.' This contingent truth needs a truth-maker, and on presentism this truth-maker must exist today. Our presentist might plausibly say that it is Sykes' footprints outside my window, and the the broken glass, both of which exist today, that tie Sykes to the crime and make-true the contingent sentence in question.  But what makes it true that my grandfather Alphonso drank a glass of dago red on New Year's Day, 1940 and pronounced it excellent?  Suppose the red wine drunk by Alphonso came from the Gallo vineyard. What now makes it true that that particular glass of dago red came from the Gallo vineyard as opposed to the Cribari vineyard? What exists now that could serve as a truth-maker of such truths?  There are plenty of past-tensed truths that have no presently existing truth-makers.  This is why Rhoda argues that it is only present facts involving divine memories that are up to the truth-making job.

Whether recourse to God and his omniscience works to save presentism we leave for later. 

Logic Quiz: Is the Argument Below Specious or Sound?

1) What I know cannot be otherwise: if I know that p, then p cannot be false.

Therefore

2) If I know that a man is walking, then 'a man is walking' cannot be false.

Therefore

3) If  I know that a man is walking, then it is necessarily true that a man is walking.

Extra credit: explain the meaning of 'specious.'

Argumentative Circles and their Diameters: More on Presuppositionalism

The day before yesterday, re: presuppositionalism, I wrote:

We need to bear in mind  that arguments have premises and that no argument can prove its own premises. An argument of the form p therefore p is an argument valid in point of logical form in which premise and conclusion are identical, but no one will take an argument of this form as proving that p. Every circular argument of the above form is valid, and some are sound; but none are probative. By that I mean that no such argument constitutes a proof.  That ought to be perfectly obvious.

'Circularity' in respect of arguments is of course a metaphor: no argument is literally a geometrical circle. But it is a useful metaphor and I propose we extend it by speaking of the 'diameter' of a circular argument.  The logical form italicized above — p therefore p — has a 'diameter' than which no shorter can be conceived.  Its 'diameter' is zero. If a geometrical circle has a diameter of zero, then it is not a circle but a point.  The diameter of a circular argument of the above form is also a 'point,' figuratively speaking, the point being the one proposition that serves as both premise and conclusion.

A circular argument of zero diameter is said to be 'vicious.' Are there then 'virtuous' or if not positively virtuous then  'non-vicious' circular arguments?  Can one argue in a way that is circular but logically acceptable? Brian Bosse brought up this issue over lunch Sunday as we were discussing my longish entry on presuppositionalism. He may have had John M. Frame in mind.

Presuppositionalists such as Frame take the Word of God as set forth in the Protestant Christian Bible as their "ultimate presupposition." (Five Views on Apologetics, Zondervan 2000, 209) It is their "ultimate criterion of truth." (209)  This commitment of theirs is faith-based:

. . . for Christians, faith governs reasoning just as it governs all other human activities. Reasoning is not in some realm that is neutral between faith and unbelief. There is no such realm, since God's standards apply to all of life. (209)

What causes faith? ". . . God causes faith by his own free grace." (209) What is the rational basis of faith? ". . . the answer is that faith is based on reality, on truth. It is in accord with all the facts of God's universe and all the laws of thought that God has ordained. . . . The faith he gives us agrees with God's own perfect rationality." (209-210)

We want to know what rationally justifies faith in God and in his Word as found in the Bible. We are told that this faith is justified because it is true, agreeing as it does with all of the laws of thought that God has ordained. God himself, as the ultimate source of all things, including rationality, is the ultimate rational justification of our faith in him and his Word.  The reasoning here is plainly circular as Frame admits:

There is a kind of circularity here, but the circularity is not vicious. It sounds circular to say that faith governs reasoning and also that it is based on rationality. It is therefore important to remember that the rationality that serves as the rational basis for faith is God's own rationality. The sequence is: God's rationality –>human faith –>human reasoning. The arrows may be read "is the rational basis for." That sequence is linear, not circular. (210)

Frame's fancy footwork here is unavailing, an exercise in sophistry. He is obviously reasoning in a circle by presupposing the very thing whose existence he wants to prove. But he is loathe to admit that this is what he is doing. So he introduces a bogus distinction between vicious circles and linear circles.  But just as 'linear circle' in geometry is a contradictio in adjecto , so too is 'linear circle' in logic. 

You are either arguing in a circle or you are not. You are either presupposing what you are trying to prove or you are not. You are either begging the question or you are not. You are either committing the formal fallacy of petitio principii (hysteron proteron) or you are not. That is the long and the short of it. One or the other and no weaseling out via some bogus distinction between vicious and non-vicious circular arguments.

What Frame wants is a 'knock-down' (rationally compelling or rationally coercive) argument for the existence of the God of the Protestant Christian Bible interpreted along Calvinist lines.  He thinks he can get what wants by way of a transcendental argument,  one that issues in God "not merely as the conclusion of an argument, but as the one who makes argument possible." (220)  He wants God to play a transcendental role as the ultimate and unconditioned condition of the possibility of all our intellectual operations including reasoning, whether valid or invalid, sound or unsound. (If his God does play the transcendental role, then Frame can say that the arguments of atheists, just insofar as they are arguments, prove the existence of God!) 

Now it must be granted, as I granted to Brian over lunch, that if Frame's God exists, then he does play the transcendental role. The question, however, is whether it can be proven that nothing other than Frame's God could play the transcendental role. It can be proven that there is a transcendental condition of all our intellectual operations. (See my earlier entry.) Where Frame goes wrong is in thinking that from the fact that there is a rationally compelling argument for the existence of a transcendental condition of the possibility of all our intellectual operations (forming concepts, defining terms, making judgments, giving arguments, replying to objections offering hypotheses, etc.) it follows immediately that his God exists beyond the shadow of a rational doubt.  How does he know that his God alone could play the transcendental role? Frame may be taxed with  giving the following invalid argument:

a) If the God of the Protestant Christian Bible exists, then he plays the transcendental role;

b) It is objectively certain that something plays the transcendental role;

ergo

c) It is objectively certain that the God of the Protestant Christian Bible  plays the transcendental role. 

The premises are true, but the conclusion does not follow from them. For it is not objectively certain that nothing other than the God of the Christian Bible could play the transcendental role. This is because no non-transcendental argument — Frame mentions the "causal argument" — for the existence of God is rationally compelling. Hence no non-transcendental God argument can assure us that the existence of God is objectively certain. 

Here is another way to see the matter. It is rationally demonstrable that there is a total and unique way things are. (For if you assert that there is no way things are, then you are asserting that the way things are is that there is no way things are.) Now if Frame's God exists, then he is the concrete and personal metaphysical ground of the way things are. But how do we know that Frame's God exists? We cannot simply assume that the transcendental proof of the existence of the way things are is also a proof of Frame's God.  So non-transcendental arguments must be brought into to take us to Frame's God, Frame's "causal argument" for example. But these arguments are none of them rationally compelling. They do not generate objective certainty. So how do we know that something else is not the metaphysical ground of the way things are?

Retorsion Revisited: How Far Does it Reach and What Does it Prove?

Retorsion (retortion) is the philosophical procedure whereby one attempts to establish a thesis by uncovering a performative inconsistency in anyone who denies it. It is as old as Aristotle and has been put to use by philosophers as diverse as Transcendental Thomists and Ayn Rand and her followers. Retorsion is something like an ad hominem tu quoque except that the homo in question is everyman, indeed every rational being. Proofs by retorsion have the following form:

Proposition p is such that anyone who denies it falls into performative inconsistency; ergo, p is true.

Suppose a person asserts that there are no assertions.  That person falls into performative inconsistency:  the propositional content of the speech act is 'inconsistent' with the performance.  *There are no assertions* is the propositional content, or content, for short.  The speech act of asserting is in this case the performance.  The inconsistency is not strictly logical, which is why I employed scare quotes.  Strictly logical inconsistency/consistency obtains between propositions, and a performance such as asserting is not a proposition.  Performances belong to the category of events, not that of propositions. And yet it is clear that there is some sort of analog of inconsistency here, some sort or analog of 'contradiction.'  The content asserted is falsified by the act of asserting it.  The performance 'contradicts' the content.

 

Continue reading “Retorsion Revisited: How Far Does it Reach and What Does it Prove?”

Nota Notae Est Nota Rei Ipsius, Kant, and the Ontological Argument

This is a re-post, redacted and re-thought, from 22 July 2011. I dust it off because something caught my eye the other morning in the Translator's Introduction to Kant's Logic. Robert S. Hartman and Wolfgang Schwarz tell us that for Kant the principle of all inference or mediate judgment is the rule Nota notae est rei ipsius nota. (p. xlii). I'm guessing that C. S. Peirce got wind of the principle from Kant. As for Hartman, I remember hearing good things about him and his work in axiology from Hector-Neri Castañeda. I also recall Hector saying that Hartman died young. Details of Hartman's eventful life here. He died at age 63, which is young for a philosopher.  Hector died at 66.

……………………………………………………………….

"The mark of a mark is a mark of the thing itself." I found this piece of scholasticism in C. S. Peirce. (Justus Buchler, ed., Philosophical Writings of Peirce, p. 133) It is an example of what Peirce calls a   'leading principle.'

Let's say you have an enthymeme:

   Enoch was a man
   —–
   Enoch died.

Invalid as it stands, this argument can be made valid by adding a premise. (Any invalid argument can be made valid by adding a premise.) Add 'All men die' and the argument comes out valid. Peirce writes:

     The leading principle of this is nota notae est nota rei ipsius.
     Stating this as a premiss, we have the argument,

     Nota notae est nota rei ipsius
     Mortality is a mark of humanity, which is a mark of Enoch
     —–
     Mortality is a mark of Enoch.

But is it true that the mark of a mark is a mark of the thing itself? There is no doubt that mortality is a mark of humanity in the following sense: The concept humanity includes within its conceptual content the superordinate concept mortal, which implies that, necessarily, if anything is human, then it is mortal. But mortality is not a mark, but a property, of Enoch. I am invoking Gottlob Frege's distinction between a Merkmal and an Eigenschaft. Frege explains this distinction in various places, one being The Foundations of Arithmetic, sec. 53. But rather than quote Frege, I'll explain the distinction in my own way using a totally original example.

Consider the concept bachelor. This is a first-order or first-level concept in that the items that fall under it are not concepts but objects. The marks of a first-order concept are properties of the objects that fall under the concept. Now the marks of bachelor are unmarried, male, adult, and not a member of a religious order. These marks are themselves concepts, concepts one can extract from bachelor by analysis. Given that Tom falls under bachelor, he has these marks as properties. Thus unmarried, etc. are not marks of Tom, but properties of Tom, while unmarried, etc. are not properties of bachelor but marks of bachelor.

To appreciate the Merkmal (mark)-Eigenschaft (property) distinction, note that the relation between a concept and its marks is entirely different from the relation between a concept and its instances. A first-order concept includes its marks without instantiating them, while an object instantiates its properties without including them.

This is a very plausible line to take. It makes no sense to say of a concept that it is married or unmarried, so unmarried cannot be a property of the concept bachelor. Concepts don't get married or remain single. But it does make sense to say that a concept includes certain other concepts, its marks. On the other hand, it makes no sense to say of Tom that he includes certain concepts since he could do such a thing only if he were a concept, which he isn't. But it does make sense to say of Tom that he has such properties as being a bachelor, being unmarried, being an adult, etc.

Reverting to Peirce's example, mortality is a mark of humanity, but not a mark of Enoch. It is a property of Enoch. For this reason the scholastic formula is false. Nota notae NON est nota rei ipsius. The mark of a mark is not a mark of the thing itself but a property of the thing itself.

No doubt commenter Edward the Nominalist will want to wrangle with me over this slight to his scholastic lore, and I hope he does, since his objections will aid and abet our descent into the labyrinth of this fascinating cluster of problems. But for now, two quick applications.

One is to the ontological argument, or rather to the ontological argument aus lauter Begriffen as Immanuel Kant describes it, the ontological argument "from mere concepts." So we start with the concept God and analyze it. The concept God includes omniscience, etc. But 'surely' existence is also contained in the concept God. For a god who did not exist would lack a perfection, a great-making property; such a god would not be id quo maius cogitari non posse. He would not be that than which no greater can be conceived. To conceive God, then, is to conceive an existing God, whence it follows that God exists! For if you are conceiving a nonexistent God, then you are not conceiving God.

Frege refutes this version of the ontological argument — not the only or best version I hasten to add — in one sentence: Weil Existenz Eigenschaft des Begriffes ist, erreicht der ontologische Beweis von der Existenz Gottes sein Ziel nicht. (Grundlagen der Arithmetik, sec. 53)  "Because existence is a property of concepts, the ontological argument for the existence of God fails to attain its goal." What Frege is saying is that the ontological argument "from mere concepts" rests on the mistake of thinking of existence as a mark of concepts as opposed to a property of concepts.  No concept for Frege is such that existence is included within it. Existence is rather a property of concepts, the property of having an instance.

The other application of my rejection of the scholastic formula above is to the logical question of the correct interpretation of singular propositions. The scholastics treat singulars as if they are generals.  But if Frege is right, this is a grave logical error since it rides roughshod over the mark/property distinction. To drag this all into the full light of day would take many more posts.

Counterexamples and Outliers

An exception to a universal generalization is a counterexample that refutes the generalization. All you need is one. Generic statements cannot, however, be similarly refuted. 'Nuns don't smoke cigars' is a generic statement. If you turn up a nun who smokes cigars I won't take you to have refuted the generic statement. I'll dismiss the exception as an 'outlier.' 

Memo to self: develop this line of thinking and then apply it to 'hot button' issues such as race. Is Candace Owens representative of black females or is she an 'outlier'? And to which generic statements is she an outlier?  You won't touch this question, will you? Not with an eleven-foot pole, which is the pole you use to touch questions you won't touch  with a ten-foot pole. 

See my aptly appellated entry, Generic Statements, for more on generic statements.

Questions about a Lukasiewicz Passage

E. B. sent this:

http://www.logicmuseum.com/wiki/Logical_form_(Lukasiewicz)

“When, for instance, asserting the implication 'If all philosophers are men, then all philosophers are mortal' you would also assert as second premiss the sentence 'Every philosopher is a man', you could not get from these premisses the conclusion 'All philosophers are mortal', because you would have no guarantee that the sentence 'Every philosopher is a man' represents the same thought as the sentence 'All philosophers are men'. It would be necessary to confirm by means of a definition that 'Every A is B' means the same as 'All A's are B's'; on the ground of this definition replace the sentence 'Every philosopher is a man' by the sentence 'All philosophers are men', and only then will it be possible to get the conclusion. By this example you can easily comprehend the meaning of formalism. Formalism requires that exactly the same thought should always be expressed by means of exactly the same series of words ordered in exactly the same manner.”

My emphasis.

Suppose we compare the following two argument displays:

If all philosophers are men, then all philosophers are mortal
All philosophers are men
—-
All philosophers are mortal.

If every philosopher is a man, then all philosophers are mortal
All philosophers are men
—-
All philosophers are mortal.

Are they both valid, or is only the first valid? Lukasiewicz is telling us in effect that only the first is valid. No doubt the first is valid: it instantiates the valid argument form, modus ponendo ponens.  But then, by my lights, so does the second. So both arguments are valid.

But it all depends on what we take an argument to be.  I hold that  an argument is not the same as an argument display. A necessary but not sufficient condition of anything's being an argument is that it be a sequence of propositions. A proposition is not the same as a sentence in the indicative mood. Die Sonne scheint and 'The sun shines' are two different indicative sentence tokens in two different  languages. And yet they 'say the same thing' or rather can be used by the same or different speakers to  say the same thing. We accommodate this fact by introducing a species of abstract object we call propositions or thoughts, the latter word used by L. above.  The sentences cited express one and the same proposition or thought.  Similarly with 'All philosophers are men' and 'Every man is a philosopher.' They express the same proposition.

So above what we have are two different ways of displaying one and the same argument.  Since that argument instantiates a valid argument form, the argument is valid.

Consider now these two argument displays:

Omnis homo mortalis est
Sokrates homo est
——-
Sockrates mortalis est.

Every man is mortal
Socrates is a man
—–
Socrates is mortal.

How many arguments? One or two? One. One and the same argument is expressed in two different languages.  I conclude that an argument is not the same a collection of sentences. Sentences are physical (marks on paper, pixels on a screen, acoustic disturbances); propositions are not. They are not seen with the eyes or heard with the ears or felt (as in Braille) with the fingers; they are understood by the mind. 

Finally, L. speaks of  exactly the same series of words ordered in exactly the same manner.  Same words in the same order? But how do we know that the words are the same? Is it because they have the same letters in the same order?  By that criterion, 'war' in the following two sentences is the same word:

Ich war ein Soldat.
I went to war.

But the two series of letters in the same order are not the same word. 

Now consider this array:

All philosophers are men.
Philosophers are, all of them, men.
Every philosopher is a man.

These sentences 'say the same thing,' i.e., they express the same proposition or thought. I know that because I understand English.  To understand English is to understand the meanings of English words and sentences.  Meanings are understood by the mind not perceived by the sense organs.

Syntactic and Semantic Validity Again

Edward sends this interesting example:

Omnis homo est mortalis

Socrates is a man

Sokrates ist sterblich

Semantically valid, but not syntactically?

No, syntactically valid because the argument instantiates a valid argument-form, to wit:

Every F is a G
a is an F
Therefore
a is a G.

Validity is a matter of form. An argument is valid if it instantiates a valid argument-form.  It is the form that is valid or invalid in the primary senses of these terms. The argument itself is valid or invalid in secondary senses. The argument inherits its validity from the form, so to speak.  Or you could say that it is the validity of the form that is the ground of, and accounts for, the validity of the argument.

For me, and here is where Ed will disagree, a valid deductive argument such as the 'Socrates' syllogism above, is a sequence of propositions, not of sentences, that instantiates a valid argument-form.

A proposition is what a sentence in the indicative mood expresses. To be precise, a proposition is what is expressed by the tokening (whether by utterance, writing, or in some other way) of a sentence in the indicative mood.   The following three sentences, each from a different language, can be used to express one and the same proposition or Fregean Gedanke (thought) :

Sokrates mortalis est.
Sokrates ist sterblich.
Socrates is mortal.

These three numerically different sentence tokens from three different languages express the same proposition when they are used to express a proposition.  Sentences are linguistic entities. Propositions are extra-linguistic, and therefore not tied to particular languages as sentences are.  Not tied in the sense that the same proposition can be expressed in different languages.  Suppose that every English speaker is exterminated. Could it then be said that Socrates is mortal? Yes, though not in those words. One could say the same thing by uttering the corresponding German or French or Turkish  sentence. 

This is a reason to distinguish propositions from sentences.  

Now glance back at Ed's example. It is linguistically hybrid.  But logically it expresses the very same argument (sequence of propositions) that the following does:

Every man is mortal
Socrates is a man
Ergo
Socrates is mortal.

The argument expressed is syntactically valid because it is an instance of a valid argument-form.