Hear from a lot of people that to cast a spell you need to hold your arcane focus in your hand. However scouring the books and any errata I can't seem to find anything actually stated officially here.
Does anyone have an actual source for this? Can it not be something just on their person?
So far only the holy symbol states that it must be held in your hand, does this mean that the others don't?
Best Answer
Yes.
You need to hold the arcane focus for it to substitute as a material component.
Spellcasting Focus Substitutes for a Material Component
To clarify: you only need to hold a spellcasting focus to cast spells with a material component, not for every spell. You can tell the difference in the spell description. Two examples, one without (Magic Missile) and one with (Major Image) a material component.
Spell Examples
Spellcasting Rules
From the spellcasting rules in Chapter 10.
Spellcasting Focus
A spellcasting focus is:
Note on the Holy Symbol:
Because it can simply be "worn visibly," the Holy Symbol is an exception; it's a spellcasting focus that doesn't necessarily need to be held. (See Do you need a free hand for your holy symbol if you're wearing it visibly?)
The Fine Print
The specific exceptions to this general rule are spells that have a material component that is consumed. Example: Resurrection.
(Finer print: A spell with a material component that isn't consumed but has a specific cost in GP (example is Identify, requires a pearl worth at least 100 gp which isn't consumed) still needs the material component).
The same rules are in the PHB.
Note: we had a discussion on what constitutes a bardic spellcasting focus here.