The rules for INT specify that the ability to reason is controlled by INT. A low INT = a low ability to reason. It's up to the player to roleplay that limitation.
Don't the rules handle this?
Eg upthread [MENTION=6787503]Hriston[/MENTION] gave the example of making a knowledge check to recall facts about the London Underground (or some other salient element of the gameworld). A PC with a low INT will suffer a penalty to that check, reflecting his/her weaker recall and reasoning abilities.
Presumably the character also suffers a penalty on attempts to decipher unfamiliar (but somewhat cognate, so in-principle decipherable) languages/dialects, and on INT-governed perception-style checks.
In other systems, I'd take such a low score as a complication that the GM could create opportunities against. In D&D, especially point buy, what's the point in the stat if their are no in game complications, where in other stats i gain benefits from higher stats like Con, Dex, Str?
The complication is that already set out by other posters: a penalty to appropriate checks.
If the game doesn't involve many such checks then of course players might trade away INT for (say) DEX. But that just strikes me as good game play: like the fact that my players, knowing I like undead and demons as antagonists, build PCs that have at least some capability against such creatures.
Conversely, if you want players not to trade away INT, isn't the answer to devise situations that will make INT matter (eg because knowledge checks will be important)?
No, but if limitations are being taken to create benefits in other stat choices, shouldn't there be in game resource management?
The rules provide the modifiers, the scores are the bounds in which the player should be considering character options. If not, why bother with scores that define the range of a character's ability ti interact with the world around them?
If you aren't going to roleplay the limits of your stats, there's no point in having numbers for them.
In 5e, isn't the score mostly just a device for allocating a bonus?
In Moldvay Basic, there was a table for INT. An INT 3 character "has trouble with speaking". A character of INT 5 or less "cannot read or write". This means that a player of a PC with INT 4 can't declare, as an action, that his/her PC reads something or writes something. And a player of a PC with INT 3 can't delcare, as an action, that she utters some complex or beautiful sentence.
But 5e doesn't have a comparable rule that I'm aware of.
The old relative scale used to be INT*10 = IQ, so yes, there is an implied implication.
Does 5e have this rule? And does it then have a rule correlating IQ to permissible action declarations?
Leaving aside doubts about the validity of IQ as a notion, I think there are bigger issues here. A MU/wizard with 5 STR is a very viable PC in a typical D&D game. S/he will suck in melee, but given that MUs tend to suck in melee anyway, that is not a great deficit. If encumbrance is used his/her max load won't be that great, but there's likely to be at least one pack-horse fighter in a typical D&D party.
In effect, the MU player is not meaningfully constrained in permissible action declarations by having a 5 STR. And while there is a range of action delcarations where the 5 STR will hurt him/her, s/he was going to be wanting to avoid those anyway because even without 5 STR s/he sucked at them.
Saying that the 5 INT fighter can't make rational action declarations, on the other hand, is coming very close to preventing the player of that character meaningfully participating in the game - except perhaps as the comic relief, or as the Hulk-like weapon who is pointed by the other PCs at the right targets when violence breaks out.
To me, that doesn't seem like a very good game rule. (Contrast, say, the Moldvay language rules, which operate in a particular domain and only affect a particular set of action declarations. INT 3 is still pretty brutal, but not as brutal as some people in this thread seem to be suggesting the much less improbable INT 5 is.)