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As the title. I've seen many definitions such as concealment refer to one or both, but I can't find a clear definition of them or how they are different.

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Here's the definition of Line of Effect:

is a straight, unblocked path that indicates what a spell can affect. A line of effect is canceled by a solid barrier. It's like line of sight for ranged weapons, except that it's not blocked by fog, darkness, and other factors that limit normal sight. A line of effect starts from any corner of your square and extends to the limit of its range or until it strikes a barrier that would block it. A line-shaped spell affects all creatures in squares through which the line passes.

And here's the definition of Line of Sight:

is the same as a Line of Effect but with the additional restriction that that it is blocked by fog, darkness, and other factors that limit normal sight (such as Concealment).

This means that when a spell has a Target entry as part of its description

You must be able to see or touch the target, and you must specifically choose that target.

And this makes spells with a Target entry require line of sight (or being able to touch the target if appropriate). But if the spell creates an effect

You must designate the location where these [effects] are to appear, either by seeing it or defining it. Range determines how far away an effect can appear, but if the effect is mobile, after it appears it can move regardless of the spell's range.

Thus making those spells require only line of effect.

For example, a fireball spell can be cast into an area of darkness into which the caster cannot see but the caster must select a point of origin for the fireball's effect that's within the spell's range and to which the caster has line of effect. On the other hand, a charm person spell must be cast on a creature to which the caster has line of sight and line of effect as that spell targets a creature specifically.

More details can be found under Aiming a Spell.

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  • \$\begingroup\$ This answer is interesting. Does that mean that line of sight is blocked by solid but invisible barriers? (e.g. a pane of glass, a wall of force) \$\endgroup\$ – gatherer818 Jul 14 '15 at 1:41
  • \$\begingroup\$ @gatherer818 Yes. Haven't met a group other than ours that plays that way, though. As a note, this means that they aren't really see-through because they block line of sight. Also note that regions of darkness block line of sight. So if you have a torch and they have a torch but there's a 10ft wide area of dark between you, you can't see each other. \$\endgroup\$ – the dark wanderer Jul 14 '15 at 2:54
  • \$\begingroup\$ @thedarkwanderer yeah, the stupidity of how light works is something I'm already familiar with, and the only reason I realized this answer meant what it does. Obviously, it's something to houserule away unless the point of your campaign IS the ridiculousness of RAW, but still... \$\endgroup\$ – gatherer818 Jul 14 '15 at 3:10
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    \$\begingroup\$ @gatherer818 That a game incorporating magic has extremely poor functionality with regards to invisible barriers is kind of funny, but, yes, a pane of glass or a wall of force does block the game's definition of line of effect therefore line of sight. But Aiming a Spell really does go into more detail, adding, "An otherwise solid barrier with a hole of at least 1 square foot through it does not block a spell's line of effect." (I've no proof, but I suppose design intent was that buildings would shutter their windows instead of using glass panes, making the quirk less of an issue.) \$\endgroup\$ – Hey I Can Chan Jul 14 '15 at 8:41
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Line of sight - I see you on the street while sitting down eating by looking through a window.

Line of effect - it ends at the window

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  • \$\begingroup\$ I want an actual rules definition, not common term definition. \$\endgroup\$ – GreySage Jul 13 '15 at 23:49
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    \$\begingroup\$ That is a rules definition, there must be nothing blocking the way for line of effect regardless of being able to see through it. So glass and force effects for instance DO block line of effect but not line of sight. \$\endgroup\$ – Fering Jul 13 '15 at 23:53
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    \$\begingroup\$ For questions concerning the "Rules-as-written" tag, its important to cite your sources for determining exactly what each definition consists of. \$\endgroup\$ – Sandwich Jul 14 '15 at 0:10
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    \$\begingroup\$ @Fering This isn't a rules definition, this is two unsupported examples of how a rules definition works in play. You need to add both the definition and some sources proving that it is the definition for this to be a good answer. \$\endgroup\$ – Miniman Jul 14 '15 at 0:29

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