If it is true today that you will read this sentence tomorrow, then tomorrow you will read it, and it can seem to follow that you have no choice about it.
That argument uses no laws of nature, no initial conditions and no neuroscience. It is older than all of them, and versions of it were being answered in Athens in the fourth century BC. Two of the arguments in this lesson fail, and they fail on a mistake that the logic course diagnoses exactly. The third does not fail so easily, and understanding why is the best possible preparation for the serious argument against free will in the next lesson.
The sea battle
Aristotle raises the problem in chapter nine of De Interpretatione, around 350 BC, with an example about a naval engagement. Take the statement "there will be a sea battle tomorrow". By the principle of bivalence, every statement is either true or false. So this one is either true or false today, before the battle. If it is true today, then the battle will occur, and no admiral's decision can prevent it. If it is false today, then it will not occur, and no admiral can bring it about. Either way, tomorrow's outcome is settled today, and the deliberations of the admirals are theatre.
The argument generalises immediately to everything anyone will ever do, which is why it matters. Note that it appeals to nothing but the truth values of statements. A world with no laws of nature at all, in which events simply happened at random, would face the same argument, provided that statements about the future have truth values.
Aristotle's own response is disputed. The traditional reading, and the one that dominated for centuries, has him restricting bivalence: statements about future contingents are neither true nor false until the matter is settled. That is a serious cost, since it means abandoning a principle that is otherwise as safe as anything in logic, and it also fails to touch the argument's real weakness. A modern treatment can do better.
The scope error
Here is the argument written out, with standing for "there will be a sea battle tomorrow" and for necessity.
First premise: is either true or false, and suppose it is true. Second premise: necessarily, if is true then there will be a sea battle. Conclusion: so if is true, then necessarily there will be a sea battle, which is to say the battle cannot be prevented.
The second premise is a truth of logic and cannot be denied: it just says that if a statement is true then things are as it says, which is what truth means. The conclusion, however, does not follow from it, and the failure is a scope error of exactly the shape the logic course flags. The premise has the form
and the conclusion has the form
and the second does not follow from the first. Medieval logicians had a name for the distinction and used it for precisely this argument: necessitas consequentiae, the necessity of the inference, against necessitas consequentis, the necessity of the thing inferred. To see the gap with a countermodel, take as "the cup is on the table". Necessarily, if the cup is on the table then the cup is on the table. It does not follow that if the cup is on the table then it is on the table necessarily, since somebody may lift it.
So the sea battle argument is invalid, and bivalence survives. What was true today was true because of what the admirals would do; the truth did not reach back and make them do it. Truth tracks the world rather than constraining it, and that phrase is the second lesson of this lesson, worth as much as the first.
Example. Diagnose this: "If I know that you are sitting down, then you cannot stand up, since if you stood up I would not have known it."
The scope error again, dressed in knowledge instead of truth. What is true is that necessarily, if I know you are sitting, you are sitting: knowledge entails truth. What does not follow is that if I know you are sitting, you are necessarily sitting, in the sense of being unable to stand. The final clause of the objection actually gives the game away: if you stood up, then I would not have known, which is exactly right and shows that my knowledge depends on your behaviour rather than the other way round. My knowing tracks what you do. It does not hold you in the chair.
Now you. A friend says that since a photograph taken yesterday shows what you were wearing yesterday, and the photograph cannot now be altered, your having worn those clothes was unavoidable. Is the argument the same one, and where does it differ?
Answer
The scope error is there, since from "necessarily, if the photograph shows a blue shirt then a blue shirt was worn" nothing follows about the wearing being necessary. But there is a further ingredient, and it is genuinely different: the appeal to the past being fixed. Yesterday's action is indeed unavoidable now, and nobody disputes that, which is why the example feels compelling and is also harmless. It becomes an argument against free will only when the fixed item lies in the past and the action it settles lies in the future, and that is the combination the foreknowledge argument constructs.
The cost of Aristotle's escape
Since the scope reply works, it is worth seeing what the traditional reply would have cost, because the comparison shows how much cheaper a logical diagnosis is than a semantic surgery.
Denying bivalence for future contingents means saying that "there will be a sea battle tomorrow" is neither true nor false today. That immediately threatens the law of excluded middle, since the disjunction of a statement with its negation should be a logical truth and here both disjuncts lack a value. It also plays badly with ordinary talk: if I say today that it will rain tomorrow and it rains, most people think what I said was true, and that it was true when I said it, not that it became true overnight.
Twentieth-century logicians built machinery to soften the damage. Richmond Thomason's supervaluational semantics of 1970 treats the future as a branching tree of possible continuations and counts a statement as true now if it is true on every branch, false if false on every branch, and neither otherwise. The disjunction "either there will be a sea battle or there will not" then comes out true on every branch and so true now, which rescues excluded middle while leaving each disjunct without a value.
That is elegant, and it is much more machinery than the problem needs. The scope diagnosis leaves classical logic untouched, keeps bivalence, and explains the illusion. When a small logical error and a large semantic revision both dissolve a paradox, the error is nearly always the right diagnosis.
Example. Under supervaluation, evaluate these three statements as spoken today: "there will be a sea battle tomorrow", "either there will be a sea battle tomorrow or there will not", and "if there is a sea battle tomorrow, ships will be lost".
The first is neither true nor false, since some branches contain a battle and others do not. The second is true, because on every branch one disjunct or the other holds, which is exactly the feature the semantics was designed to deliver. The third is true if on every branch where a battle occurs ships are lost, which is a substantive claim about naval warfare rather than about logic, and the point of including it is that conditionals about the future are not automatically valueless: only the contingent parts go silent, and the structure connecting them survives.
Now you. Does denying bivalence actually save free will?
Answer
Not on its own, and this is the strongest reason not to buy the machinery. Suppose statements about the future have no truth value today. The Consequence Argument of a later lesson needs no such statements: it uses a description of the past, which is as determinate as anything, plus the laws, plus an entailment. If determinism holds, the past and the laws entail what you will do, and the entailment does not care whether anyone has uttered a prediction or whether that prediction has a truth value now. Aristotle's repair addresses the semantics of prediction, and the serious threat to freedom does not come from predictions.
The idle argument, briefly
The other ancient argument was mentioned in the previous lesson and can be dealt with quickly. If you are fated to recover, you will recover whether or not you call the doctor; if you are fated not to, you will not, whether or not you call; so calling is pointless.
The reply, attributed to Chrysippus in the third century BC, is that outcomes and actions are co-fated. If it is fated that you recover, it may equally be fated that you call the doctor, and the recovery comes about through the call rather than in spite of it. The fatalist's dilemma assumes that each branch is settled independently of what you do, and neither is.
The reason the idle argument is worth a paragraph is that its error is the one people actually make when they first meet determinism. They hear "the future is fixed" and conclude "so nothing I do matters", which reverses the actual implication: on a deterministic picture what you do matters completely, and is itself fixed.
Foreknowledge, which is harder
Now the argument that does not dissolve. It comes from theology, and it was stated in its modern form by Nelson Pike in 1965, but its interest is entirely independent of whether anyone believes in the foreknower.
Suppose there is a being who is essentially omniscient, so that it not only knows everything but could not be mistaken. Eighty years ago, that being believed that you would read this sentence today. Now assemble three claims. The past is fixed: nothing anyone does now can change what was the case eighty years ago. An essentially omniscient being cannot hold a false belief. And if you were to do otherwise now, then that past belief would have been false.
Put together, the argument concludes that you cannot do otherwise. And note what has happened: the scope reply no longer works. The argument does not move from "necessarily, if it was believed then it will occur" to "it will necessarily occur". It moves from a fixed fact about the past, together with an entailment, to a fixed fact about the present. That is a different and much better argument.
Look at its skeleton, because you will meet it again in the next lesson. It has a fixity premise, that the past is not up to us; a connection premise, that the past item entails what you do now; and a transfer principle, that what is entailed by something not up to us is itself not up to us. Change "God's belief eighty years ago" to "the state of the world eighty years ago and the laws of nature" and you have the Consequence Argument almost word for word. The theological version is the dress rehearsal, and it has been rehearsed for sixteen centuries.
Example. Which premise of the foreknowledge argument does the following reply attack: "God is outside time altogether, so there is no moment at which God's belief lies in the past"?
The fixity premise, by denying that the belief has a temporal location at all. This is the reply of Boethius in the sixth century and of Aquinas in the thirteenth: an eternal being sees all times at once, as a person on a hill sees a whole road that a traveller on it experiences in sequence, so God's knowledge is not earlier than your action and the fixity of the past does not apply to it. The standard objection is that the argument can be rebuilt without the temporal ordering: if a timeless fact entails what you do, and that fact is not up to you, the transfer principle still delivers the conclusion. Moving the knower out of time removes one premise and leaves the shape intact, which is a good sign that the shape rather than the theology is what matters.
Now you. The Ockhamist reply distinguishes hard facts about the past from soft ones. Which of these two is soft, and why does the distinction matter here: "Caesar crossed the Rubicon in 49 BC", or "Caesar crossed the Rubicon 2074 years before this lesson was read"?
Answer
The second is soft. It is stated as a fact about 49 BC, but its truth depends on something that happens much later, namely this lesson being read now, so it is not purely about the past. William of Ockham's suggestion in the fourteenth century, revived in the twentieth, is that God's past belief about your future action is soft in exactly this way: it is a fact about the past whose content depends on the future, and the fixity premise applies only to hard facts. The dispute since has been over whether a clean criterion for hardness can be given, and the leading attempts, from Marilyn Adams onwards, have all had trouble. The reply is respectable and unfinished, which is roughly the state of every reply in this subject.
What these arguments leave behind
Three results carry forward, and they are the tools for reading the next lesson.
The first is the scope distinction. Any argument that concludes from a necessary connection that one of its terms is necessary should be symbolised before it is believed, and most such arguments will not survive the symbolising. This is the most common single defect in bad arguments against free will, and spotting it takes ten seconds once the habit is there.
The second is the difference between tracking and constraining. A true statement, a photograph, a diary entry and an infallible belief all match the world without pushing it. That someone knows what you will do is a fact about them, not a chain on you. When we come to the empirical evidence, the same point returns in scientific dress: a brain signal that predicts your choice is tracking your decision-making, and only a further argument makes it a constraint on you.
The third is the shape that does survive. Fixity, connection, transfer. Nothing in that skeleton commits a scope error, and nothing in it confuses tracking with constraining. It is the best argument against free will that anyone has produced, and in its secular form, using nothing but the past and the laws of nature, it has dominated the field since 1983. That is the next lesson.