Lois Lane has the following two beliefs
(1) that Clark Kent cannot fly, and that Superman can fly.
Yet Clark Kent and Superman are identical. Substituting ‘Superman’ for ‘Clark Kent’ in the first belief gives us the beliefs
(2) that Superman cannot fly, and that Superman can fly.
Clearly it is irrational to hold the beliefs characterised by (2). Does this mean that Lois has irrational or illogical beliefs in believing (1)? Or is the inference from (1) to (2) invalid? Contra: the beliefs characterised in (1) are clearly not irrational. For we base our beliefs on evidence. The evidence given to us in the Superman stories suggests that Clark Kent and Superman are identical. The reader is always shown evidence that Clark Kent is Superman, by means of scenes showing him changing from his office suit and glasses to his Superman costume, without glasses. The same stories show us that Lois Lane does not have the benefit of this evidence. She is looking the other way, or is looking for shoes or handbags while Clark is changing his costume. Therefore
(3) The reader of the stories has evidence that Clark Kent is Superman
(4) Lois Lane does not have evidence that Clark Kent is Superman
Therefore, I argue, it is not irrational for Lois to have the beliefs expressed by (1). It is not irrational to believe that of which one has no evidence to the contrary – even though other people, such as the reader, have evidence to the contrary. Therefore the inference from (1) to (2) is invalid.
Note, and this is actually is my main point against Eric’s position here, that it is invalid for exactly the same reason that the following inference is invalid.
(5) Lois Lane has evidence that Superman can fly, therefore she has evidence that Clark Kent can fly.
The puzzle about substitution and belief statements is the same as the puzzle about substitution and evidence statements. Even though Clark Kent is identical with Superman, the evidence that Clark Kent is Superman is different from the evidence that Clark Kent is identical with himself.