“Real” doesn’t mean “flesh and blood”, does it? Hobbes can be real and think thoughts and have ethics way beyond Calvin’s capacity without being breathing flesh and blood.
Spaceman Spiff is imaginary.
And, oh, side note. I hate the way Red and Rover tries to rip off Calvin and Hobbes with the time machine.
C&H exist in an artificial universe. And I don’t mean on the comics page. There’s the “real world” and spun off via a mysterious, possibly psychotic, process from that is the C&H universe. So Hobbes is “real” in that alternate universe. But the rules of that universe are that only Calvin can see him “in action”. So the mother and others also are as “real” as Hobbes within that universe.
Well, to be fair, I think it takes a pretty willful disregard for the meaning/intent of the work (or lack of comprehension) to honestly ask the question “does Hobbes actually magically come to life?”
Of course Hobbes is “just” a stuffed tiger (and the transmogrifier is “just” a cardboard box, etc etc etc). That doesn’t mean any of the thoughts/stories/experiences that Calvin has are less honest or true than those that involve Mrs. Wormwood the teacher (as opposed to Mrs. Wormwood the monster).
That’s the blurred line in Calvin and Hobbes, not whether anything in it is actually real or not, but whether or not the imagination is important or frivolous; whether or not we can find value and truth in fantasy.
ETA: my first sentence sounds a little snarky, and it’s not meant personally . . . I just think that if one thinks that Hobbes actually comes to life than one is struggling with comprehension of the comic strip.
As TreacherousCretin sez, Hobbes is a Phooka, who is seen as a stuffed tiger to everyone but Calvin. No one but Calvin can see him, but they can sometimes see the results, such as cookies eaten, Calvin messed up after a “tiger attack”. , etc
Hobbes has an independent existence: while he and Calvin share a special friendship, Hobbes doesn’t seem to me to be a particularly credible imaginary friend. For one thing he’s a lot smarter than Calvin. He certainly doesn’t agree with Calvin all or even most of the time. They have consistently different outlooks.
As noted upthread, Hobbes is cartoon-real: he’s as real as the falling anvils that (temporarily) turn Wile E Coyote into an accordion. The transmorgrifier and the planets where Calvin and Hobbes have their adventures are also real: they just aren’t accessible by the other characters in the strip, who perceive an odd kid playing with a stuffed animal. Nothing wrong with that: Watterson has stated that the strip is partly about differing perspectives.
Anyway, those are 2 of the main themes in Calvin and Hobbes: friendship and differing perceptions.
ETA: T-Rex in F-14. Not all that real, actually. T-Rex Jet | Know Your Meme