Why is "or" working but "and" is not in my Ember.ComputedProperty?

I think I'll feel stupid once I see the answer, but I can't wrap my head around why or is working but and isn't on this ComputedProperty. The tutorial suggested I'd need to use and, but I can't figure out how I'd do that if this doesn't work.

To start with I am new to Ember and familiar but not really comfortable with javascript, which is why I assume I'm having difficulty understanding what is going on here.

I have two properties that I need to both be true before a button isDisabled. I pass each of them to their own properties that reverse their boolean state so isDisabled remains active on a button until the original properties are both flipped.

contact.js

emailAddress: '',
  message: '',

  //**original properties**
  isValid: Ember.computed.match('emailAddress', /^.+@.+\..+$/),//starts as false
  validMessage: Ember.computed.gte('message.length', 5),//starts as false

  //**my reversing boolean properties**
  notYet: Ember.computed.not('isValid'),//starts as true
  notNow: Ember.computed.not('validMessage'),//starts as true


//isDisabled must be true to be active disabling button
  isDisabled: Ember.computed.or('notYet', 'notNow'),//starts as true

If I put in the correct emailAddress format:

emailAddress = true
notYet = false
isDisabled = true //still

If I then put a validMessage of 5 characters or more

  validMessage = true
  notNow = false
  isDisabled = false //now

Why does "or" work for this, why doesn't "and" or "not"?