Learn Hardcore German: Weil sein Abiturzeugnis so gut war, konnte er Medizin studieren. - Because his high school diploma was so good, he was able to study medicine.

sein Abiturzeugnis so gut war
- war (was) is the verb, so it goes to the end.
Word order pattern:
[weil] + Subject + (objects/adverbs) + Verb

So:

Weil sein Abiturzeugnis so gut war
not: Weil war sein Abiturzeugnis so gut (wrong)

Why is it konnte er Medizin studieren and not er konnte Medizin studieren?

In a main clause that follows a weil-clause, the verb still must be in second position. The entire weil-clause counts as position 1, so the finite verb of the main clause comes next, before the subject:

Weil sein Abiturzeugnis so gut war, konnte er Medizin studieren.
- Position 1: Weil sein Abiturzeugnis so gut war,
- Position 2 (verb): konnte
- Then subject: er
- Then rest: Medizin studieren

If you start with the main clause instead, you get normal word order:

Er konnte Medizin studieren, weil sein Abiturzeugnis so gut war.

Why is it war and konnte (simple past) instead of forms with haben (perfect tense)?

Both war (was) and konnte (was able to / could) are in the Präteritum (simple past).

German often prefers the simple past for:

sein, haben
modal verbs (können, müssen, dürfen, etc.)
written language and narratives

You could say:

… ist so gut gewesen, hat Medizin studieren können,
but that sounds heavier and is much less natural in everyday German than:
… so gut war, konnte er Medizin studieren.

What exactly does Abiturzeugnis mean?

Abiturzeugnis is a compound noun:

Abitur = final school examinations qualifying for university (roughly: A‑levels / high school diploma level)
Zeugnis = report card, certificate

So Abiturzeugnis = the final school certificate you get after passing the Abitur, usually needed for university admission.

sein Abiturzeugnis = his Abitur certificate / his school‑leaving certificate.

Why is sein Abiturzeugnis in the nominative case?

In the weil-clause, sein Abiturzeugnis is the subject of the verb war (was).

Basic pattern:

Subject (nominative) + sein (to be) + complement

Here:

Subject: sein Abiturzeugnis
Verb: war
Predicate adjective: so gut

So it must be nominative:

Sein Abiturzeugnis (nominative) war so gut.

Why is it so gut and not sehr gut?

Both so gut and sehr gut are possible, but they have slightly different nuances:

sehr gut = very good (a factual, direct statement about quality)
so gut = so good (often highlighting a consequence, inviting a following clause: because it was so good, …)

In this sentence, so gut fits well because it leads naturally into the result:

Weil sein Abiturzeugnis so gut war, konnte er Medizin studieren.
Because his certificate was so good, he was able to study medicine.

Why is there no article before Medizin? Why not die Medizin studieren?

Academic subjects in German are usually used without an article when you mean studying that subject at university:

Er studiert Medizin.
Sie studiert Jura.
Wir studieren Physik.

Using an article would change or sound odd:

die Medizin = the medicine, more like the medical science / the medical substance, not the general field of study as a university subject in this context.

So Medizin studieren (no article) is the natural phrase for to study medicine (at university).

Why is it Medizin studieren and not Medizin lernen?

German distinguishes between:

studieren = to study at a university / to major in
lernen = to learn / to study in the sense of doing homework or memorizing

For university programs, you normally use studieren:

Er studiert Medizin / Physik / Germanistik.
Sie studiert Jura.

Medizin lernen would sound unusual here and would not carry the meaning of being enrolled to study medicine at university.

Why does Medizin come before studieren and not after it?

In a clause with a modal verb (here: konnte) and an infinitive (here: studieren), word order is:

Modal verb in second position
Other elements (objects, adverbials)
Infinitive at (or near) the end

So:

konnte (modal, position 2)
er (subject)
Medizin (object)
studieren (infinitive at the end)

→ konnte er Medizin studieren

In German main clauses with modal verbs, the main infinitive always goes to (near) the end.

Why is it er and not ihn or ihm?

er is the nominative singular masculine personal pronoun and is used for the subject of the clause:

Subject: er
Verb: konnte
Object: Medizin (what he could study)

ihn would be accusative (direct object), ihm dative (indirect object), but here he is the one doing the action (he could study), so er is required.

What is the difference between weil and denn for “because”? Could I say Denn here?

Both weil and denn can mean because, but they behave differently:

weil:
- Subordinating conjunction
- Sends the verb to the end of its clause
- Can come before or after the main clause
Example:
- Weil sein Abiturzeugnis so gut war, konnte er Medizin studieren.
- Er konnte Medizin studieren, weil sein Abiturzeugnis so gut war.
denn:
- Coordinating conjunction
- Does not change word order
- Connects two main clauses
Example:
- Er konnte Medizin studieren, denn sein Abiturzeugnis war so gut.

You cannot start the sentence with Denn sein Abiturzeugnis war so gut, konnte er… in the same structure; that’s ungrammatical. With denn, you would say:

Er konnte Medizin studieren, denn sein Abiturzeugnis war so gut.

Why is there a comma after the weil‑clause?

German requires a comma between main clauses and subordinate clauses:

Weil sein Abiturzeugnis so gut war, (subordinate clause)
konnte er Medizin studieren. (main clause)

So you must separate them:

Weil sein Abiturzeugnis so gut war, konnte er Medizin studieren.

Likewise, if you reverse the order:

Er konnte Medizin studieren, weil sein Abiturzeugnis so gut war.

Why are Abiturzeugnis and Medizin capitalized?

In German, all nouns are capitalized.

Abiturzeugnis is a noun (a thing → a certificate) → capitalized.
Medizin is also a noun (medicine, the field or substance) → capitalized.

This is a regular rule, not special to this sentence:

das Haus, die Stadt, die Liebe, der Computer, etc.