A chair

Authoring Inform 7
1

How do I make a chair sittable and standable?

Edit: I figured it out:

A chair is a kind of supporter. A chair is always enterable.
In the red room is two chairs.

2

In TADS 3 you just need to use a Chair object:

+Chair 'sturdy chair/seat' 'sturdy chair'
    "It definitely looks like it can take your weight. "
;

In Inform 7, postures aren’t included by default, but the recipe book includes an example of how to add them:

http://inform7.com/learn/man/Rex346.html#e346

In real life you’ll need to learn carpentry:

http://www.woodworking4home.com/ChairPlans.php