1. Philosophy of Science Lars-Göran Johansson Department of philosophy, Uppsala University lars-goran.johansson@filosofi.uu.se

2. Knowledge: Scientific and other Two forms of knowledge: Two forms of knowledge: Knowing that: the content of a belief. Knowing that: the content of a belief. Knowing how: an ability Knowing how: an ability Belief-contents can be expressed by declarative sentences! Belief-contents can be expressed by declarative sentences!

3. Knowing that – knowing how Compare: Compare: Peter knows that Berlin is the capital of Germany Peter knows that Berlin is the capital of Germany Susan knows how to ride a bicycle Susan knows how to ride a bicycle N.B. The content of a belief is expressed by a complete sentence, the ability with a verb-phrase only. N.B. The content of a belief is expressed by a complete sentence, the ability with a verb-phrase only.

4. A posteriori- a priori knowledge A posteriori- a priori knowledge Knowledge a priori: knowledge which is independent of our senses Knowledge a priori: knowledge which is independent of our senses Knowledge a posteriori: knowledge which ultimately depends our senses. Knowledge a posteriori: knowledge which ultimately depends our senses. Mathematical and logical knowledge consists of knowledge a priori Mathematical and logical knowledge consists of knowledge a priori

5. Plato’s definition of knowing that X knows that p if and only if X knows that p if and only if –P is true –X have good reasons for p –X believes p

6. Truth Why make truth a condition of knowledge? Why make truth a condition of knowledge? Isn’t knowledge simply everything we believe with good reasons? Isn’t knowledge simply everything we believe with good reasons? No. No. What’s the point of asking for knowledge, if truth is not the goal? What’s the point of asking for knowledge, if truth is not the goal? Knowledge is more than mere opinion Knowledge is more than mere opinion We are interested in more than beliefs; we want to know the facts! We are interested in more than beliefs; we want to know the facts!

7. Truth Minimal requirement on the concept of truth: Minimal requirement on the concept of truth: ‘p’ is true if and only if p ‘p’ is true if and only if p In other words: In other words: To say about a statement that it is true is the same as to ascertain that statement To say about a statement that it is true is the same as to ascertain that statement

8. Theories of truth Correspondence Correspondence Coherence Coherence Pragmatist Pragmatist Minimal or deflationary Minimal or deflationary

9. Beliefs To belief something is a mental state To belief something is a mental state If we accept that a necessary condition for knowledge is belief, then no thing that lacks mentality can have knowledge. If we accept that a necessary condition for knowledge is belief, then no thing that lacks mentality can have knowledge. Could a machine have knowledge? Could a machine have knowledge? Could an animal have knowledge? Could an animal have knowledge?

10. Good reasons Good reasons may be of two forms: Good reasons may be of two forms: Justification Justification Evidence Evidence (OBS. This is a distinction made by some philosophers; in ordinary discourse no distinction is made.) (OBS. This is a distinction made by some philosophers; in ordinary discourse no distinction is made.)

11. Justification Justification is a relation between beliefs Justification is a relation between beliefs If you believe a proposition p and is asked for its justification, you should provide another proposition q, (or a set of propositions). If you believe a proposition p and is asked for its justification, you should provide another proposition q, (or a set of propositions). The proposition q justifies p The proposition q justifies p Typical example: mathematical proofs Typical example: mathematical proofs

12. Proof A proof is a sequence of statements A proof is a sequence of statements The sequence begins with one or several assumptions and ends with the proved sentence. The sequence begins with one or several assumptions and ends with the proved sentence. Suppose A, B and C are the premises in the proof of Q, i.e., Suppose A, B and C are the premises in the proof of Q, i.e., A, B, C ⊢ Q A, B, C ⊢ Q Then: A, B and C together completely justifies Q! Then: A, B and C together completely justifies Q!

13. Justification outside math and logic: Ex: scientific laws The general law of gases, pV=nRT, is justified by a sentence expressing that a portion of gas satisfying this equation. The general law of gases, pV=nRT, is justified by a sentence expressing that a portion of gas satisfying this equation. More instances increases the justification of the general law. More instances increases the justification of the general law. But no amount of instances will prove it. But no amount of instances will prove it. Justifcation is not complete Justifcation is not complete

14. Inductive reasoning Inductive reasoning proceeds from singular statements to a general statement, sometimes a scientific law. Inductive reasoning proceeds from singular statements to a general statement, sometimes a scientific law. More instances makes the conclusion more trustworthy; but complete justification is never attained. More instances makes the conclusion more trustworthy; but complete justification is never attained. Inductive reasoning is uncertain. Inductive reasoning is uncertain. We cannot prove anything by inductive reasoning! We cannot prove anything by inductive reasoning!

15. Observation- belief When we perform an experiment we observe certain outcomes. When we perform an experiment we observe certain outcomes. Most often we immediately believe the propositions expressing these observations. Most often we immediately believe the propositions expressing these observations. But observing the outcome and believing the proposition describing the outcome are different things. But observing the outcome and believing the proposition describing the outcome are different things. We can imagine saying ‘I see x, but I don’t believe it! ’ We can imagine saying ‘I see x, but I don’t believe it! ’

16. Observation - belief The belief in a proposition expressing an observation may justify another proposition, for example a scientific law. The belief in a proposition expressing an observation may justify another proposition, for example a scientific law. But the observation cannot justify the proposition expressing the observation! But the observation cannot justify the proposition expressing the observation! For an observation is not a belief; For an observation is not a belief; –I saw Zlatan in city yesterday –I believe Zlatan was in city yesterday

17. Observation - Belief To observe something does not require any judgement. To observe something does not require any judgement. Observation is perceptual experience. Observation is perceptual experience. We may occasionally doubt what we observe; We may occasionally doubt what we observe; We judge whether to believe the content of the observation or not! We judge whether to believe the content of the observation or not! Hence, observing that p and believing that p are different things. Hence, observing that p and believing that p are different things.

18. Observation- -belief From the movie ‘A beatiful mind’: From the movie ‘A beatiful mind’: John Nash is approached by a person outside the lecture hall. Nash asks one of his students: “Do you see this man?” John Nash is approached by a person outside the lecture hall. Nash asks one of his students: “Do you see this man?” Obviously, Nash doubts his observation. Obviously, Nash doubts his observation. His reason for doing so: he has schizophrenia and knows that he sometimes hallucinate. His reason for doing so: he has schizophrenia and knows that he sometimes hallucinate.

19. Evidence –the relation between observations and beliefs Following Susan Haack: Following Susan Haack: The relation between an observation and a belief is an evidential relation The relation between an observation and a belief is an evidential relation An observation provides evidence for the belief: An observation provides evidence for the belief: I observe an elk in front of the the wood, and that is evidence for my belief that there is an elk in front of the wood. I observe an elk in front of the the wood, and that is evidence for my belief that there is an elk in front of the wood.

20. Good reason-Justification- Evidence A certain belief is justified by other beliefs A certain belief is justified by other beliefs This leads to an endless regress, unless This leads to an endless regress, unless –There are some beliefs that justifies themselves, or –There are some beliefs that do not need justification. Our good reasons for some beliefs consist in observational evidence, not that they are justified!

21. Good reason-Justification- Evidence A belief is justified by other beliefs A belief is justified by other beliefs The chains of justification ends with beliefs for which no other justifying beliefs exist. The chains of justification ends with beliefs for which no other justifying beliefs exist. Our good reasons for these beliefs consist in us having empirical evidence for them Our good reasons for these beliefs consist in us having empirical evidence for them

22. Analogy- crossword puzzle The starting points for the solution of a crossword puzzle are the clues. The starting points for the solution of a crossword puzzle are the clues. When we are in the process we use letters from earlier guessed words as additional help. When we are in the process we use letters from earlier guessed words as additional help. Analogy: clues – observational evidence Analogy: clues – observational evidence Letters from earlier guessed words - other beliefs giving evidence. Letters from earlier guessed words - other beliefs giving evidence.

23. Analogy- crossword puzzle The correctness of the solution judged by The correctness of the solution judged by –Reasonable connection between clues the their corresponding items –Everything fits together Analogy: a true theory must both be supported by observational evidence and be coherent. Analogy: a true theory must both be supported by observational evidence and be coherent.

24. Justifcation in logic and math Axioms in mathematics are not justified; neither do we have evidence for them. Axioms in mathematics are not justified; neither do we have evidence for them. But how can we say we know them? But how can we say we know them? Axioms may be viewed as implicit definitions of the concepts used in stating them. Axioms may be viewed as implicit definitions of the concepts used in stating them. A priori knowledge is knowledge about usage of concepts. A priori knowledge is knowledge about usage of concepts.