Sive legatum sive fideicommissum scribitur, signator tabulas obsignat.

Sive ... sive is a correlative conjunction. It means whether ... or or either ... or.

So:

• sive legatum sive fideicommissum scribitur = whether a legacy or a fideicommissum is written

It presents two alternatives, but the main clause applies in either case.

They are both in the nominative singular, because each one can serve as the subject of scribitur.

In other words, Latin is really saying:

• sive legatum scribitur
• sive fideicommissum scribitur

Both nouns are alternatives to each other, so they appear in the same form.

Also, both are neuter second-declension nouns, and for neuter nouns the nominative singular and accusative singular look the same, ending in -um.

Because sive ... sive presents the nouns as alternatives, not as a combined plural subject.

The sense is:

• whether a legacy is written
• or a fideicommissum is written

Each option is singular, so the verb is singular: scribitur = is written.

If Latin meant that both things together were being written as a plural subject, a plural verb would make more sense, but that is not what this sentence is doing.

Scribitur is:

• 3rd person singular
• present tense
• passive voice
• indicative mood

from the verb scribere = to write

So literally it means is written.

The sentence focuses on the thing being written, not on the person writing it.

So Latin says:

• legatum scribitur = a legacy is written
• not someone writes a legacy

This is very natural Latin. The agent is either unknown, unimportant, or simply not mentioned.

Not necessarily. In a sentence like this, the present tense often expresses a general rule, habit, or customary procedure.

So the idea is closer to:

• whenever a legacy or fideicommissum is written, the signator seals the tablets

rather than only right now, at this moment.

Signator is the nominative singular subject of obsignat.

So:

• signator = the person doing the action
• obsignat = seals

In other words, the signator seals.

The noun itself means something like signer, sealer, or witness who seals/signs, depending on context.

Tabulas is accusative plural, the direct object of obsignat.

So:

• signator tabulas obsignat = the signator seals the tablets

Why plural? In Roman contexts, legal documents were often written on tablets (for example, multiple wax tablets tied together). So the plural is perfectly natural.

Also, tabulae can refer not just to physical tablets, but to the document itself as embodied in those tablets.

Obsignat is the 3rd person singular present active indicative of obsignare.

It means:

• seals
• seals up
• affixes a seal to

The prefix ob- adds the idea of sealing over or securing something formally. So obsignare is stronger and more specific than simply marking or writing.

Latin word order is much more flexible than English word order because the endings show the grammatical roles.

English depends heavily on position:

• the signator seals the tablets

Latin can move the words around more freely:

• signator tabulas obsignat
• tabulas signator obsignat
• obsignat signator tabulas

All of these could work, though they may differ in emphasis.

Here, the sentence begins with the whether ... or clause, setting up the condition first, and then gives the main action.

Yes. Grammatically, both are second-declension neuter nouns.

That means they follow the normal neuter pattern:

• singular nominative/accusative: -um
• plural nominative/accusative: -a

So forms like these are what you would expect from regular neuter nouns of that declension.

Yes. A learner may see tablets and think only of physical objects, but in Roman legal language tabulae often means the written legal document as preserved on those tablets.

So depending on context, English might say:

• tablets
• document
• will
• written instrument

The Latin still literally says tabulas, but the practical sense can be broader than just the wooden or wax tablets themselves.