The Physical Language as the Universal Language of Science 101

Carnap's explicit development of protocol sentences roughly coincides with the syntactic turn of his philosophy. This was the time in which he came to believe that all of the significant features of a sentence, including its truth value, could be found in its syntax - a view we briefly contrasted with Schlick's position in the previous chapter.

By the time of "Physical Language…" (1932a, [1934a]) Carnap had been persuaded by Tarski of the importance of the distinction between object language and metalanguage (Uebel, 2007, p.142). This comes out explicitly in Carnap's distinction between the material and the formal modes of speech, which Carnap runs alongside each other in separate columns. The material mode of speech talks about objects and states of affairs, while the formal mode of speech talks only about words and sentences. For example, we might say in the material mode of speech that arithmetic is the study of the properties of numbers, but in the formal mode of speech we would say that sentences of arithmetic are made up of signs of such-and- such a kind, put together in such-and-such a way, and can be transformed according to such-and-such rules. Carnap believes that "a philosophical investigation must be an analysis of language" (1932a, [1934a, pp.37-38]) and so the formal mode of speech is, strictly speaking, the correct one. The material mode of speech employs statements which only make sense within the object language, but the formal mode of speech employs statements in the metalanguage.

Carnap draws attention to three possible views that one could have about the nature of protocol sentences, and, in 1932, does not attempt to choose between them.21 _{On the first view, protocol sentences are of the form "here now blue, there}

red", and the objects of protocol statements are, in the material mode of speaking,

21_{In “Uber Protokollsatze”, written after Neurath’s criticisms and published at the same time}

(still in 1932), he argues that the three possible views are actually compatible with one another and

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the "simplest sensations and feelings" (p.46), not whatever physical things may or may not have caused them. On this conception, the word "blue" in the protocol sentence "here, now, blue," does not refer to some property of some object in some external world - it refers to the speaker's mental state at the moment of utterance. Carnap attributes this position to Ernst Mach.

The second view is that what is actually recorded in a protocol sentence should be some complex of current experience. Depending on which proponent of the view you were speaking to, this could mean either some partial region of one's perceptual (e.g. visual or aural or ...) field, the entirety of that perceptual field, or the entirety of experience across all perceptual fields at the same time. Sentences like "here, now, blue," can be derived from protocol sentences by isolating a certain part of the speaker's current experience, but they are not strictly speaking protocol sentences themselves. This is the view which Carnap says was held by the majority of people at the time. The distinction between this view and the first one is that experiences at individual points – the experiences which would be described by

“here now red” for instance – have to be isolated from the given protocol. This view was adopted by many positivists in response to results in Gestalt psychology which appeared to show that our experience is something other than the sum of many individual points (Carnap, 1932a, [1934a, p.47]).

The third view is that protocol statements have essentially the same form as statements like "the red cube is on the table". On this view, the objects of protocol sentences are objects of the external world. A protocol sentence is not a sentence about one's direct sense experience, but about what it is that one is currently experiencing. Carnap says that this view was not widely held at the time, but we shall see in the next section that it is (at least, close to) the view that was soon to be advocated by Neurath. That Carnap was willing to entertain this view as an option is already a step towards the view he would eventually adopt - in the earliest draft of the paper, from around mid-1930, the only options considered were the phenomenal ones (Uebel, 2007, p.188).

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However we think of protocol sentences, Carnap says that they must be translatable into sentences of the physical language - that is, the language which expresses what properties of the world are in what place at what time. The protocol sentences themselves were to be formed in a separate language, called the "protocol language". The physical language is the language of science, and because science is not meant to have "merely subjective interpretation but sense and validity for all subjects who participate in it" (1932a [1934a, p.66]), the language must be intersubjective. That means that words like "red" in the physical language don't correspond to a specific private sensation (as they do on the most common interpretation of the protocol language), but to properties in the physical world like "the colour at such-and-such position on the colour chart". If there was a machine which spoke out loud any colour at which it was pointed then a blind man could work out where certain colours were and could use the words "red" or "blue" in the physical language, even though they would not appear in his protocol language because they could only ever be obtained indirectly.

In addition to being intersubjective, the physical language is supposed to be universal. That is to say, "every statement (whether true or false) can be translated into it" and "every possible state of affairs (every conceivable state, whether actually occurring or not) can be expressed by it" (Carnap, 1932a, [1934a, p.67]). If a statement cannot be translated into the physical language, then it is not verifiable and is therefore a pseudo-statement. That includes protocol statements. Carnap says that "every statement in the protocol language can be translated into a physical statement and indeed into one which describes the state of S's body" (1932a, [1934a, pp.87-88]) - this link between the epistemically privileged sentences in the protocol language and the sentences in the physical language was supposed to be the epistemic foundation of the system of science. However, this step introduced a problem. Protocol sentences were supposed not to require verification (or, at least, they were supposed to be undoubtedly true and immediately verified for whoever was formulating the protocol sentence) but any statement about the state of your body will be open to disconfirmation - an ardent sceptic could even maintain without contradiction that you might be a disembodied consciousness undergoing

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utterly unreal hallucinations. It is this weakness that Neurath attacked in Protokollsatze (1932, [1959]).