Rules Clarification: "Spells Known"

The adventure gods frowned upon the DM in the most recent session for his lack of vigilance in ensuring the company's spell casters adhered to the rules regarding spell knowledge--an issue the DM himself undoubtedly exacerbated through his experimentation with hastily-drafted house rules.  But a review of the relevant Players Handbook sections provides as follows:

• Warlocks (p. 107): a warlock starts out knowing two 1st-level spells of the player's choice and learns additional spells as the character levels up according to the table on PH pg. 106.  When a warlock levels up, he or she may also replace known spells with different spells from the warlock list.  Warlocks do not need to prepare spells; they simply know them, and can cast spells as long as they have slots available (a warlock recovers his or spell slots on completing a short or long rest).

• Sorcerers (p. 101): like warlocks, sorcerers start out with two 1st-level spells and learn more as they go up in level, per the chart on PH pg. 100.  Sorcerers may also swap known spells for new spells as they level.  Unlike warlocks, sorcerers must complete a long rest to regain their spell slots.

• Wizards (p. 114): a wizard character begins with six 1st-level spells in his or her spell book at 1st level, and adds two spells of the player's choice (of a spell level the character can cast) at each level increase thereafter.  In addition, wizards may add spells they discover on scrolls or other in-game sources to their spell books (see PH pg. 114).  Unlike warlocks and sorcerers, however, wizards must prepare spells to cast them; this requires both a long rest and access to their spell books.   

• Clerics (p. 58): like wizards, clerics must prepare their spells ahead of time to cast them.  But instead of being limited to the spells available in a book, a cleric can choose any spell from the cleric list.  A cleric will also have a few spells permanently prepared, based on the cleric's divine domain.  

• Druids (p. 66): druids follow the same basic rules as clerics: they must prepare their spells ahead of time but can choose any spells from the druid list.  

• Others: characters of certain other classes can sometimes cast spells (e.g., rangers, certain rogues and fighters, etc.).  The rules appear to vary slightly for each of these but generally they appear to follow the sorcerer/warlock rules--"knowing" a small number of spells rather than compiling them in a spell book.

Clarification of established house rule:

• Wizards still prepare spells ahead of time, in accordance with their spell slot allotments.  However, a wizard may also attempt to cast an unprepared spell, provided the spell is in the wizard's book.  An unprepared spell will have a chance of failure.  The DM regrets not making clear previously the requirement for a wizard spell to be in the wizard's book in order to be cast unprepared.

Adjudications:

• Any spell that a wizard has already cast at any previous point in the game shall be deemed already contained in that wizard's spell book.  These spells shall not count against the wizard's base allotment (of six first-live spells, plus two spells per level increase).

• All wizards' spell books shall automatically contain the spells read magic and detect magic.  These spells shall not count against the wizard's base allotment.

New house rules under consideration:

• Possible increase in the number of spells that warlocks and sorcerers know at any given point (to allow knowledge of 2-4 spells per spell level).  This would seem to add more variety to the game without significantly enhancing the power of such spell casters.  

• Possible revision of cleric spell lists based on specific deities.  (That is, instead of a single spell list for all clerics, each deity would have a list of spells available to clerics of that particular faith).  This is another rule intended to provide variety and flavor to the game without significantly affecting character class balance.

Comments on any of the proposed changes (or other recommendations) are welcome and invited!