Learn Hardcore Croatian: Ne vidim veliku razliku između ta dva načina učenja. - I do not see a big difference between those two ways of learning.

Context decides which one is meant. So you don’t add any special word for “a” here; you just say “veliku razliku” and let the situation make it clear.

Why is it “veliku razliku” and not “velika razlika”?

The verb vidjeti (“to see”) takes a direct object in the accusative case.

Dictionary forms: velik (adjective “big”), razlika (noun “difference”).
Nominative (the “dictionary” form): velika razlika – “a big difference”.
Accusative feminine singular: veliku razliku – this is used as the direct object.

So, because “a big difference” is the thing you see / don’t see, it must be in the accusative:

(Ja) vidim veliku razliku. – I see a big difference.
(Ja) ne vidim veliku razliku. – I don’t see a big difference.

The adjective veliku and noun razliku both change to the accusative and must agree in gender, number and case.

Why is it “učenja” and not “učenje” in “načina učenja”?

“Način učenja” literally means “way of learning”.

Croatian often uses the genitive case on the second noun to express “of” in English:

način učenja – way of learning
vrsta hrane – type of food
knjiga matematike – book of mathematics

The dictionary form is učenje (neuter noun “learning”), but in “načina učenja” it is in the genitive singular: učenja.

So “ta dva načina učenja” literally is “those two ways of learning”, with učenja showing that it’s “ways of learning”.

What case does “između” take, and how does that affect “ta dva načina učenja”?

The preposition između (“between”) always takes the genitive case.

Examples:

između kuća – between (the) houses
između mene i tebe – between me and you
između ta dva grada – between those two cities

In “između ta dva načina učenja”:

The whole phrase “ta dva načina učenja” is governed by između, so it functions in the genitive.
načina is in the genitive (its form after dva is the same as its genitive singular).
učenja is also in the genitive singular, as explained earlier.
The forms ta and dva don’t visibly change here, but they belong to a phrase that is in the genitive after između.

So grammatically this is “between those two ways of learning”, with između + genitive.

Why is it “ta dva načina” and not “tih dvaju načina”? Are both possible?

Both are possible, but they differ in style and frequency:

ta dva načina – very common, neutral, everyday Croatian.
tih dvaju načina – grammatically correct, but feels formal / bookish and is not what people usually say in casual speech.

Some notes:

ta here is the demonstrative (“those”), used with numbers like dva, tri, četiri.
dva is the numeral “two” used with masculine and neuter nouns.
načina is the required form of način after dva.

So your sentence “Ne vidim veliku razliku između ta dva načina učenja” sounds natural and standard in everyday language.
A very formal writer might choose “između tih dvaju načina učenja”, but learners don’t need to use that form.

Why is there no “ja” in front of “ne vidim”? When do Croatians drop the subject pronoun?

Croatian is a “pro-drop” language: the verb ending usually shows who the subject is, so the personal pronoun is often omitted.

Vidim. – I see.
Vidimo. – We see.
Ne vidim. – I don’t see.

You add ja only for emphasis or contrast:

Ja ne vidim veliku razliku, ali ti možda vidiš.
I don’t see a big difference, but you might.

So in your sentence, “Ne vidim veliku razliku…” is the normal, neutral version.
“Ja ne vidim veliku razliku…” would stress that it’s you personally who doesn’t see it.

Can the word order change? For example, can I say “Ne vidim između ta dva načina učenja veliku razliku”?

Croatian word order is fairly flexible, but some orders sound more natural than others.

Your original sentence is the most neutral:

Ne vidim veliku razliku između ta dva načina učenja.

Other possible orders:

Između ta dva načina učenja ne vidim veliku razliku.
Emphasises the phrase “between those two ways of learning”.
Ne vidim veliku razliku među ta dva načina učenja.
(here also changing the preposition; stylistically less usual but possible in some contexts).

The version:

Ne vidim između ta dva načina učenja veliku razliku.

is understandable, but it sounds a bit clumsy and less natural, because the direct object “veliku razliku” is pushed to the end. Speakers strongly prefer to keep “veliku razliku” right after “ne vidim” in this kind of sentence.

What is the difference between “između” and “među”? Both can look like “between/among”.

Both prepositions can overlap in meaning, but there is a typical preference:

između – “between” two or a small, clearly separated number of things:
- između ta dva načina učenja – between those two ways of learning
- između kuće i škole – between the house and the school
među – “among / amidst” many things or within a group:
- među ljudima – among people
- među studentima – among (the) students

Because you are explicitly talking about two ways, između ta dva načina učenja is the most natural choice.
You usually wouldn’t use među directly with “ta dva” in this sentence.

How can I say “I don’t see any big difference” or “I don’t see any difference at all”?

You can strengthen the negation with words like nikakav (“no, any at all”) or nikakvu in the correct form:

Ne vidim nikakvu razliku između ta dva načina učenja.
I don’t see any difference at all between those two ways of learning.

If you keep “big”, you can say:

Ne vidim nikakvu veliku razliku između ta dva načina učenja.
I don’t see any big difference between those two ways of learning.

You might also hear:

Ne vidim neku veliku razliku između ta dva načina učenja.
Literally “I don’t see some big difference”, meaning “I don’t really see much of a big difference” (softer, more hedged).

How would the sentence change if I wanted to say “I don’t see big differences between those two ways of learning” (plural “differences”)?

You need the plural of “difference” in the accusative:

Singular: veliku razliku – a big difference.
Plural: velike razlike – big differences (here accusative plural feminine).

So the sentence becomes:

Ne vidim velike razlike između ta dva načina učenja.
I don’t see big differences between those two ways of learning.

Only veliku razliku → velike razlike changes; the rest of the sentence stays the same.