@JeremyECrawford @_FoxyBoxes_A wizard can cast a spell learned from Magic Initiate (see the Sage Advice Compendium).
they still can't cast it using a spell slot unless they chose their class for the feat; Ranger is out of luck.

— Ken Livingston (@undrhil) August 29, 2015

@undrhil @_FoxyBoxes_ The EK and the ranger can cheat (RAW) because of how their features are worded. But what you say is RAI.

— Jeremy Crawford (@JeremyECrawford) August 29, 2015

@_FoxyBoxes_ Last question: is this ‘cheating’ a problem balance-wise? It's not a balance problem per se. It's a fairness problem, which many players perceive as a balance problem. @undrhil

— Jeremy Crawford (@JeremyECrawford) August 30, 2015

@_FoxyBoxes_So nothing will break if I rule it to be castable by anyone with spell slots? Will something in the system break? No. Will someone think it's unfair? Maybe. @undrhil

— Jeremy Crawford (@JeremyECrawford) August 30, 2015

@shadowbladespaiCan a monk add his WiS bonus to his CA if it has a Mage armor spell active? Many thanks for your help!! Different AC calculations don’t stack, so a monk can’t simultaneously benefit from Unarmored Defense and mage armor.

— Jeremy Crawford (@JeremyECrawford) January 7, 2015

Can you jump farther than your movement when using magic i.e spell Jump & boots of striding and springing?

@mikemearls @Plaguescarredi’d rule yes – design intent is to make you jump super far To be clear, things like the jump spell don’t increase speed. You can jump crazy far, but your speed caps it.

— Jeremy Crawford (@JeremyECrawford) September 17, 2014

@Plaguescarred @mikemearlsAre you saying you can’t jump farther than your speed even with Jump spell or Boots of Striding and Springing? Every foot jumped costs movement, so you can jump farther than your current speed if you take the Dash action.

— Jeremy Crawford (@JeremyECrawford) September 18, 2014

@Lancekepnerdoes a rogue with arcane trickster count as wizard class for attunement to staff of fire? An arcane trickster isn't considered a wizard. @mikemearls

— Jeremy Crawford (@JeremyECrawford) March 17, 2015

Must I doff a shield to use it as an improvised weapon?

@dpnorton “Must I doff a shield to use it as an improvised weapon?” Nope. It’s shield-bash time!

— Jeremy Crawford (@JeremyECrawford) February 12, 2015

Does proficiency with my shield apply to a shield bash? Why doesn’t every monster with a shield detail a bash?

@dpnorton If you attack with a shield, it’s a normal improvised weapon, unless a special feature says otherwise. @SeldenNeil

— Jeremy Crawford (@JeremyECrawford) February 13, 2015

@dpnorton The Dueling feature makes some assumptions about imp. weapons that aren’t in the text. I’ll explain in Sage Advice.@MLenser

— Jeremy Crawford (@JeremyECrawford) February 13, 2015

@Criminal_Bizzybut under trance PHB says “After resting in this way, you gain the same benefit that a human does from 8 hours of sleep.” Sleep isn't the same thing as a long rest. Elves don't need sleep, but they do need downtime to regain their strength.

— Jeremy Crawford (@JeremyECrawford) January 7, 2015

@Criminal_BizzyPHB says that a long rest is “at least 8 hours long, during which a character sleeps or performs light activity:” = Trance The intent is that Trance replaces sleep, not the light activity that can fill part of a long rest.

— Jeremy Crawford (@JeremyECrawford) January 7, 2015

@ShooplessCan you use the spell sniper feat to grab the Shillelagh spell? How about Thorn Whip? Spell Sniper allows you to learn thorn whip, which includes an attack roll, but not shillelagh, which doesn't.

— Jeremy Crawford (@JeremyECrawford) August 26, 2014