Are "only" and "just" always interchangeable?

Question

In an English lesson, that can be edited by users, there's a dicussion about a sentence to translate.

This sentence is:

I just eat pasta.

To mean "I only eat pasta".
My own opinion is that this sentence is very ambiguous, because it looks like "I just ate pasta".
I'm not a native, so I need advice from native users.
What a native would use? Rather "just" in this case or "only".

The persons who think this sentence is a good sentence, argue that "only" is interchangeable with "just".

I think it's one of the exception, but is it?

Answer 1

"Is only and just always interchangeable?"

No. "He is a just man" cannot be changed to "He is an only man."

(Here the placement of the "a" makes all the difference, because "He is just a man" would mean "He is only a man.")

Just can mean fair or upright. And just can mean only. Just can also mean recently.

So just is only interchangeable with only where it is meant to be interchangeable with only.

My own opinion is that this sentence is very ambiguous, because it looks like "I just ate pasta".

To a native speaker "I just eat pasta" and "I just ate pasta" are nothing alike. Only the past tense is ambiguous for just. Because "I just ate pasta" could mean "All I ate was pasta" or it could mean "I ate pasta a few minutes ago." But "I just eat pasta" can only mean "I only eat pasta," if it is stated by a native speaker. If a non-native speaker says "I just eat pasta" then it can be ambiguous due to non-native speakers sometimes using present tense as past.

Answer 2

"just" has many definitions and uses. 4a in Google's on-line dictionary is the use the OP is thinking of. In my experience you might hear this use, but it is just a bit substandard. In other words, if "just" means "only," use "only."

Google

just jəst/ adjective adjective: just; superlative adjective: justest

1.
based on or behaving according to what is morally right and fair.
"a just and democratic society"
synonyms: fair, fair-minded, equitable, even-handed, impartial, unbiased, objective, neutral, disinterested, unprejudiced,

open-minded, nonpartisan; More honorable, upright, decent, honest, righteous, moral, virtuous, principled "a just and democratic society" antonyms: unfair (of treatment) deserved or appropriate in the circumstances. "we all get our just deserts" synonyms: deserved, well deserved, well earned, earned, merited; More rightful, due, fitting, appropriate, suitable; formalcondign; archaicmeet "a just reward" antonyms: undeserved (of an opinion or appraisal) well founded; justifiable. "these simplistic approaches have been the subject of just criticism" synonyms: valid, sound, well founded, justified, justifiable, warranted, legitimate "just criticism" antonyms: unfair, wrongful

adverb adverb: just

1.
exactly.
"that's just what I need"
synonyms: exactly, precisely, absolutely, completely, totally, entirely, 

perfectly, utterly, wholly, thoroughly, in all respects; "she's just right for him" exactly or almost exactly at this or that moment. "she's just coming" 2. very recently; in the immediate past. "I've just seen the local paper" synonyms: a moment ago, a second ago, a short time ago, very recently, not long ago "I just saw him" 3. barely; by a little. "I got here just after nine" synonyms: narrowly, only just, by a hair's breadth; More barely, scarcely, hardly; informally the skin of one's teeth, by a whisker "we just made it" 4. simply; only; no more than. "they were just interested in making money" synonyms: only, merely, simply, but, nothing but, no more than "she's just a child" really; absolutely (used for emphasis). "they're just great" synonyms: really, absolutely, completely, positively, entirely, totally, quite; More indeed, truly "the color's just fantastic" used as a polite formula for giving permission or making a request. "just help yourselves" possibly (used to indicate a slight chance of something happening or being true). "it might just help" 5. British expressing agreement. "“Simon really messed things up.” “Didn't he just?”"

Thus you can say I ate only pizza (and not salad); I just finished eating pizza (thus I'm no longer hungry); Only I ate pizza (other people ate salad); and I eat only pizza (nothing else).

Answer 3

This sounds like Asian language basic mix up, as they will use English to say ''I just eat pasta '' meaning 'I just ate pasta' - but this is not correct .

The tenses are very important in English and can have an affect on the implication of the other words in the sentence, such as in this case.

Meaning is vital.

No one 'just' or 'only' eats nothing but pasta ...

However

''Did you enjoy the buffet?'' or ''Have you eaten already'' might both elicit the reply

a) ''I just ate pasta.''

You could also say

b)''I only ate pasta'' interchangeably

;-)

but only in this example.

If you asked why someone doesn't want to eat what you offer, they COULD potentially reply

c) ''I just ate pasta'' as a reason, and it would mean something completely different

It (C) would mean ''I am full because I ate (pasta) recently''

Whereas in example a) the same sentence meant ''I didn't eat much''