Чай с мёдом слаще чая без мёда.

with

Breakdown of Чай с мёдом слаще чая без мёда.

• чай: the tea
• без: without
• мёд: the honey

Questions & Answers about Чай с мёдом слаще чая без мёда.

Why is с мёдом in the instrumental case but без мёда in the genitive?

Because in Russian different prepositions govern different cases:

• с (“with”) always takes the instrumental, so мёд → мёдом.
• без (“without”) always takes the genitive, so мёд → мёда.

Why don’t we use чем (“than”) and a comma before чая без мёда?

Russian comparatives have two forms:
1) With чем + nominative, e.g. слаще, чем чай без мёда (requires a comma).
2) By omitting чем and putting the second term in the genitive, e.g. слаще чая без мёда (no comma).
The sentence uses the second, shorter pattern.

How is слаще formed from сладкий, and why not сладнее?

Сладкий has an irregular comparative: its root changes слад- → слащ- plus -е → слаще.
Сладнее is not the standard comparative for сладкий (though you might hear dialectal сладче, the literary form is слаще).

Why is there no article before чай (like “the” or “a”)?