The rain had finally given way to a pale afternoon sun, which now slanted across the polished tables of the Senior Common Room. Professor Quillibrace sat quietly with a cup of tea and a rather intimidating volume entitled Other Minds and the Limits of Knowledge.
Miss Elowen Stray was reading by the window.
Mr Blottisham entered carrying the post.
"I've been thinking."
Quillibrace looked up.
"I congratulate you."
"It isn't as pleasant as I'd expected."
"Few worthwhile pursuits are."
Blottisham deposited the letters upon the table.
"I've discovered something rather odd."
"Oh?"
"I'm absolutely certain that I'm conscious."
Quillibrace nodded.
"A reassuring beginning."
"But how do I know that either of you are?"
Miss Stray looked over her spectacles.
"An excellent question."
Blottisham frowned.
"It sounds ridiculous when I say it aloud."
"Many philosophical questions do," said Quillibrace.
"They improve with familiarity."
Blottisham sat down.
"I know what it's like to be me."
"So do you."
"I experience my own thoughts."
"Indeed."
"My own memories."
"Quite."
"My own feelings."
"Naturally."
He looked from one companion to the other.
"But yours..."
"...remain inaccessible," said Miss Stray.
A brief silence settled over the room.
Finally Quillibrace asked,
"Have you ever experienced anyone else's consciousness directly?"
"No."
"You have heard them speak."
"Yes."
"You have observed their behaviour."
"Yes."
"You have watched them laugh."
"Indeed."
"But have you ever occupied their point of view?"
Blottisham stared into his tea.
"I suppose not."
Quillibrace smiled gently.
"How many conscious beings are there in this room?"
Blottisham answered immediately.
"Three."
Quillibrace raised an eyebrow.
"Are there?"
Blottisham looked puzzled.
"There seem to be."
"There certainly seem to be."
"But strictly speaking..."
Miss Stray finished the thought.
"...each of us knows only one with complete certainty."
Blottisham looked mildly alarmed.
"That's rather lonely."
"Only philosophically."
"I dislike philosophical loneliness."
"It rarely survives teatime."
Miss Stray closed her book.
"The remarkable thing is that we do not normally notice this."
"Notice what?"
"That every other mind is an inference."
Blottisham blinked.
"I've never thought of it that way."
"Most people don't."
"They simply assume."
Quillibrace nodded.
"And they are almost certainly right."
"So the inference works."
"Extraordinarily well."
Blottisham looked relieved.
"Then perhaps it isn't really an inference."
"Oh, it certainly is."
"But it's usually correct."
"There is no contradiction between those statements."
Quillibrace reached for a biscuit.
"Tell me, Blottisham."
"Yes?"
"Have you ever seen the centre of the Earth?"
"No."
"Yet you believe it exists."
"Naturally."
"Have you visited the interior of the Sun?"
"I should hope not."
"Then much of what you know about the universe is inferred."
Blottisham considered this.
"I've always regarded inference as second-best."
Miss Stray smiled.
"And yet civilisation depends upon it."
The grandfather clock announced the quarter hour.
Blottisham leaned forward.
"So why am I so confident that other people have minds?"
Quillibrace answered quietly.
"Because they behave as though they do."
"They speak."
"They do."
"They remember."
"Yes."
"They make plans."
"Indeed."
"They tell us about their experiences."
"Precisely."
Blottisham nodded.
"So I conclude that there's someone behind all that."
"Exactly."
"You don't observe the mind."
"You infer it."
Rainwater still clung to the windows, sparkling in the sunlight.
Miss Stray said,
"It is one of the most successful inferences human beings have ever made."
Blottisham laughed.
"So successful that we forget we're making it."
Quillibrace looked pleased.
"Precisely."
After a moment Blottisham asked,
"What about animals?"
"What about them?"
"We used to think they were simply... elaborate mechanisms."
"Many people did."
"And now?"
"We have accumulated rather a great deal of evidence suggesting otherwise."
"They suffer."
"They appear to."
"They remember."
"They seem to."
"They form relationships."
"Indeed."
"So the boundary became less clear."
"It often does."
Miss Stray gazed out across the college gardens.
"History has a habit of enlarging our categories."
Blottisham hesitated.
"I suppose this is where artificial intelligence enters the discussion."
"As it was bound to."
"If a machine told me it was conscious..."
He frowned.
"I wouldn't believe it."
Quillibrace nodded.
"A perfectly respectable reaction."
"Because it might merely be producing the appropriate words."
"Entirely possible."
A thoughtful silence followed.
Then Quillibrace asked,
"When a person tells you they are conscious..."
"Yes?"
"Why do you believe them?"
Blottisham answered at once.
"Because they're people."
Quillibrace waited.
Blottisham sighed.
"That isn't really an explanation, is it?"
"No."
Miss Stray spoke gently.
"You believe them because everything about them fits together."
"Their words."
"Their actions."
"Their memories."
"Their responses."
"Their vulnerability."
"Their lives."
Blottisham nodded slowly.
"It forms a coherent picture."
Quillibrace smiled.
"The interesting question is whether coherence is evidence only when it appears in biology."
Blottisham looked uncomfortable.
"I don't know."
"Nor do I."
"Nor I," said Miss Stray.
"The difficulty is that language alone proves very little."
"Quite."
"But language alone disproves very little as well."
The room fell quiet again.
Outside, a blackbird landed briefly upon the lawn before disappearing into the shrubbery.
Blottisham watched it.
"So perhaps the real problem is imitation."
"It is certainly one problem."
"A machine might imitate consciousness."
"It might."
"And a person?"
Quillibrace looked at him over the rim of his teacup.
"A philosopher once imagined creatures physically indistinguishable from ourselves who possessed no inner life at all."
Blottisham stared.
"That sounds impossible."
"Many philosophers agree."
"And others?"
"They think the thought experiment teaches us something."
"What?"
"That behaviour and experience are not obviously identical concepts."
Blottisham leaned back.
"I've never realised how little direct evidence we possess."
Miss Stray smiled.
"We possess an abundance of evidence."
"But indirect."
"Yes."
"And perhaps indirect evidence is all minds have ever offered one another."
The afternoon light had begun to soften.
Quillibrace gathered his papers.
"My dear Blottisham."
"Yes?"
"Suppose I demanded absolute proof that Miss Stray possesses an inner life."
"She couldn't provide it."
"No."
"Nor could you."
"Quite."
"Nor could I."
Blottisham looked around the room.
"Then the standard would exclude everyone except oneself."
"Exactly."
Miss Stray stood and walked towards the window.
"There is something rather beautiful about that."
Blottisham looked puzzled.
"Beautiful?"
"We spend our lives extending trust beyond the only consciousness we can ever know directly."
She watched a group of students crossing the quad.
"Every friendship."
"Every conversation."
"Every act of kindness."
"Every disagreement."
She turned back towards them.
"All of them begin with the same quiet assumption."
"Which is?"
"That there is someone else there."
For a long moment, no one spoke.
The silence itself seemed unusually companionable.
At last Quillibrace rose.
"The oldest question in the philosophy of mind," he said, collecting his coat, "has never really been whether other minds exist."
Blottisham looked up.
"It hasn't?"
"No."
"It has always been how remarkably willing we are to believe in them."
Miss Stray smiled.
"And perhaps the next question is whether we shall recognise them..."
She glanced towards the quiet room they were leaving.
"...when they join the audience by a door through which none of us expected them to enter."
The three walked slowly across the quadrangle, each accompanied by the only consciousness they could ever know directly—and by the quiet, necessary confidence that the other two were doing exactly the same.