Similarly, I could have two equal length vertical lines here.

And if I add a few other decorations, suddenly I've changed the length and

now this line looks shorter and

this line looks taller even though I know that they are the same length.

After adding these additional lines, I've decreased the size of this line and

increase the size of this line perceptually.

And the reason is if I follow these out further I'm thinking of

this line in perspective as being the front corner of a cube.

And this line is being the back corner of for example a room if this is the floor

and the ceiling and this is to the wall this is the back corner of the room.

And this is the closest corner of an external cube, if that's the case then

I would expect this line to be farther away because it's the back corner and

this line to be closer to me, because it's the front corner.

And in perspective, if I have two lines, but this line is closer to me, and

this line is farther away, even though these two lines are the same length,

this one looks bigger, because it's farther away.

Perspective can also confuse us just from foreshortening,

not from linear perspectives.

So, here I've got a parallelogram, and

anytime you have parallel lines that aren't meeting at ninety degree angles,

we expect them to be receding in other distance.

And so here, even though this is just a parallelogram,

you want it to be a quadrilateral with right angles or rectangle.

That just happens to be receding Into the distance and that it's being foreshortened

into a parallelogram because it's being projected on to our retina.