Defining Full Telepathy vs. Limited Telepathy

I've been working on a pretty significant new d30-related book—well, really books... plural (more to come in future posts). And I realized I was assigning creatures as having Telepathy or Limited Telepathy, without really knowing what that actually means. For example, many AD&D Monster Manual creatures are noted as having "limited telepathy" but never really describe what that means—like the lammasu... "Lammasu communicate in their own tongue, the language of lawful good, and through a limited form of telepathy."

Okay... so what are the limits?

They got better about this in 2e, but I set out to define Full Telepathy vs. Limited Telepathy (particularly for how it would be treated in my House Rules). So here goes...

FULL TELEPATHY

Full Telepathy supports full and clear mental communication with other creatures with very few restrictions.

• Usable at will. Full Telepathy, as an inherent ability (vs. a spell-like ability) is usable at will.
• Sentience is required. In order for the communication to take place, the target creature must have an intelligence of at least 1.
• No common language is needed. The telepath and the target need not share a common language.
• Two-way communication is supported. Full telepathy is always two-way, allowing for a conversation.
• A longer range is achievable. The standard range for Full Telepathy is 90'.
• Sighting isn't required. Full Telepathy allows for the telepath to “sense” the presence of other minds within range and target them directly.
• Communication is possible to select multiple creatures at once. The telepath can communicate with as many eligilbe targets within the range as they choose, but only one message may conveyed at a time (that is, the telepath may not conduct multiple conversations at once, unless otherwise described for that individual telepath). 
• Communication is quicker than normal speech. Full telepathy allows for the conveyance of abstract concepts beyond simple words, allowing for much quicker communication (particularly over the linear limitations of speaking and the rudimentary nature of Limited Telepathy).
• Concentration is not required. The telepath is usually able to perform other physical actions (e.g., combat, use of a breath weapon) while using Full Telepathy. Spellcasting, however, is typically prohibited while communicating telepathically (given the verbal component required). Full Telepath does not, however, hinder the use of spell-like abilities (that don’t require the verbal components of spellcasting).

LIMITED TELEPATHY

Limited Telepathy has any number of specific restrictions that kept it from being as versatile as Full Telepathy. The following limitations are common, but all of them need not apply, nor are they limited to the ones noted below.

• Usable at only certain times or under certain conditions: Though commonly usable at will, the use of Limited Telepath may have limitations that constrain when, where, and how often it may be used (e.g., in the Astral Plane, 3×/day, for 10 minutes every hour, etc.)
• Higher Intelligence Requirement: Like Full Telepathy, order for the Limited Telepathy to take place, the target creature must have an intelligence of at least 1. However, a higher Intelligence (e.g., 3 or greater) may be required.
• Shared language required: The telepathy functions only if both creatures share a common language. This may be the most common limitation.
• One-way communication: Under this circumstance, the telepath is able to either: a) send thoughts, emotions, or images to another creature, but not receive them in return; or b) understand the meaning of a speaker’s words, even if the telepath doesn’t speak the same language.
• Limited to simple concepts: Some forms of Limited Telepathy are limited to conveying only simple ideas, feelings, or images rather than complex thoughts or conversations.
• Species-specific: In such cases, the telepathy only works between members of the same species.
• Limited range: The distance over which the telepathy operates may be significantly shorter (e.g., as little as 10').
• Sighting required: The telepath may need to be able to see the target in order to communicate with (or, at a minimum, to establish the connection with) them.
• Limited recipients: Typically, Limited Telepathy is confined to conversation with a single creature at a time.
• Concentration required: If concentration is required, the telepath may undertake no other physical actions at the same time, or the telepathic connection will be lost.

Unless otherwise stated for a creature entry that includes Limited Telepathy, assume that a noted limitation restricts only that condition, and otherwise functions as Full Telepathy (e.g., "Limited Telepathy: shared language required." would function as Full Telepathy, except the telepath and target(s) must share a language.