Learn Hardcore Russian: Он объясняет, что таблетка не всегда решает проблему. - He explains that a pill does not always solve the problem.

Он объясняет, что… = He explains (that)…
The part что таблетка не всегда решает проблему depends on объясняет, so it is a subordinate clause.
Rule of thumb: if you can translate что as that introducing a clause, you usually need a comma before it.

Why is the verb объясняет (imperfective) used here, not объяснил (perfective)?

Объяснять / объяснить is an aspect pair:

объяснять – imperfective (process, repeated, general)
объяснить – perfective (single completed act, result)

Он объясняет suggests:

either he is in the process of explaining now
or this is something he does generally (e.g. in a talk, article, lecture)

Он объяснил, что таблетка не всегда решает проблему would mean:

He explained that the pill does not always solve the problem (he has already finished explaining; the action is completed).

In English we might say He is explaining… or He explains…. Which one is Он объясняет… closer to?

Russian present tense often covers both English present simple and present continuous.

Он объясняет… can mean:

He is explaining… (right now, in progress), or
He explains… (in general, for example as part of a lecture or article).

Context decides which English form is best; Russian doesn’t distinguish them with separate tenses.

Why is таблетка in the nominative, but проблему in the accusative?

Because таблетка is the subject of решает, and проблему is its direct object.

таблетка (Nom.) не всегда решает… – the pill (subject) doesn’t always solve…
решать что? – to solve what? → проблему (Acc.)

So the pattern is:

Subject in nominative: таблетка
Verb: решает
Direct object in accusative: проблему

How does не всегда work here? Does it mean “never,” “rarely,” or something else?

Не всегда literally means “not always.”

Logical meaning:

Sometimes the pill solves the problem.
Sometimes it does not solve the problem.

It does not mean “never.”

Compare:

таблетка не всегда решает проблему – the pill does not always solve the problem (sometimes it does)
таблетка никогда не решает проблему – the pill never solves the problem (it doesn’t work at all)

Could we say всегда не решает проблему instead of не всегда решает проблему?

No, that would sound very unnatural and the meaning changes.

не всегда решает проблему – does not always solve the problem (sometimes yes, sometimes no).
всегда не решает проблему is almost never used; if taken literally, it would mean something like always does not solve the problem, which is confusing and unidiomatic.

Russian uses не всегда for “not always,” just like English word order not always (not always not).

Why is что used here and not чтобы or что бы?

Here что is a simple conjunction meaning that, introducing a statement:

Он объясняет, что… – He explains that…

Чтобы is used for purpose or desired result:

Он объясняет, чтобы все поняли. – He explains so that everyone understands.

Что бы (two words) is usually что + бы (particle), used in more complex constructions (questions, wishes, etc.) and is not appropriate here.

So in this sentence, only что (meaning “that”) is correct.

Why is the word order таблетка не всегда решает проблему and not something like таблетка решает проблему не всегда?

The most natural and neutral order is:

таблетка не всегда решает проблему

This puts не всегда directly before the verb решает, making it clear that the frequency of solving is limited.

Other orders are possible but have different nuances or sound awkward:

таблетка решает проблему не всегда – possible, but sounds a bit heavier and more marked, often with emphasis on не всегда at the end.
не всегда таблетка решает проблему – focuses on “not always” first, a bit more contrastive.

The given sentence is the most standard, neutral word order.

Why is решает in the 3rd person singular, and does it show gender of таблетка?

Решает is 3rd person singular present tense:

(кто? что?) таблетка → она → решает

In the present tense:

verbs show person and number (1st/2nd/3rd, singular/plural),
but they do not show gender.

So:

он решает – he solves
она решает – she solves
оно решает – it solves

All use the same form решает. The fact that таблетка is feminine is shown only by the noun itself (its ending, agreement with adjectives, etc.), not by the present-tense verb form.

Could we say таблетки не всегда решают проблему instead? What’s the difference?

Yes, you can say:

Таблетки не всегда решают проблему.

Difference:

таблетка не всегда решает проблему – a singular used in a general, generic sense (a pill / the pill in general does not always solve the problem).
таблетки не всегда решают проблему – emphasizes pills in general, plural, or “pills” as a category (various pills, medications).

Both can be generic, but the singular таблетка is very common in Russian for making general statements about a type of thing.

Can the subject Он be omitted in Russian here?

Yes, it can be omitted if the subject is clear from context:

Он объясняет, что таблетка не всегда решает проблему.
or simply: Объясняет, что таблетка не всегда решает проблему.

Russian is a “pro-drop” language for personal pronouns: the verb ending (-ет in объясняет) already shows 3rd person singular, so if the identity of he/she/it is clear from context, the pronoun is not strictly necessary.