Tot libri in mensa iacent ut discipuli eos numerare vix possint.

Tot means so many (or simply so many/many in a counting sense), and it is indeclinable, which means it does not change its form for case, gender, or number.

So in tot libri:

• tot = so many
• libri = books

Even though libri is masculine nominative plural, tot stays tot.

This is normal Latin usage:

• tot libri = so many books
• tot puellae = so many girls
• tot dona = so many gifts

Libri is the subject of iacent.

The basic structure is:

• libri iacent = the books are lying

Since books are the thing doing the action/state of lying, Latin puts libri in the nominative plural.

Also, iacent is plural, so it agrees with libri:

• liber iacet = the book is lying
• libri iacent = the books are lying

Because this sentence expresses location, not motion toward something.

With in:

• in + ablative = in/on a place, indicating where
• in + accusative = into/onto a place, indicating motion toward

So:

• in mensa = on the table / on a table
• in mensam = onto the table

Here the books are already there, so Latin uses the ablative: mensa.

Yes. In Latin, in with the ablative can mean in or on, depending on context.

With a surface like a table, in mensa is commonly understood as on the table.

Latin often uses in more broadly than English does. English distinguishes:

• in the box
• on the table

Latin may use in for both kinds of location, depending on the noun and context.

Iacent comes from iacere, meaning to lie, to be lying, or to lie scattered.

So libri in mensa iacent gives a more vivid picture than just libri in mensa sunt.

Compare:

• libri in mensa sunt = the books are on the table
• libri in mensa iacent = the books are lying on the table

The second suggests physical position more clearly, almost as if the books are spread out there.

This is a result clause.

The sentence has this pattern:

• tot ... ut ... = so many ... that ...

So:

• Tot libri ... ut discipuli eos numerare vix possint
• There are so many books ... that the students can scarcely count them

This is different from a purpose clause.

• purpose: ut = in order that
• result: ut = so that / with the result that

Here the clue is tot. Words like tot, tam, ita, sic, adeo, tantus often introduce a result idea.

Because ut result clauses normally take the subjunctive in Latin.

So after the main clause, Latin uses:

• ut ... possint

not

• ut ... possunt

This does not mean the action is unreal. It is simply the standard grammar of a result clause.

Also, because the main verb iacent is present, the subjunctive is also present:

• main clause present → result clause often present subjunctive

So possint is exactly what you would expect here.

Because possum means to be able, and in Latin it normally takes a complementary infinitive.

So:

• possunt numerare = they are able to count
• vix possint numerare = they can scarcely count

In this sentence:

• discipuli = subject
• possint = can / are able
• numerare = to count

This is very similar to English can count or be able to count.

Eos is the direct object of numerare.

It refers back to libri:

• libri = books
• eos = them

Since libri is masculine plural, the pronoun is also masculine plural:

• nominative plural: ei / ii
• accusative plural: eos

So:

• discipuli eos numerare = the students to count them

Latin could sometimes leave the object understood from context, but using eos makes the reference explicit.

The pronoun must agree with the noun it refers to, not with its role as an object.

The noun libri is:

• masculine
• plural

So the pronoun referring to it must also be:

• masculine
• plural

Because it is the object of numerare, it takes the accusative form:

• eos

So its form is determined by two things:

1. gender/number from its antecedent (libri)
2. case from its function in the sentence (direct object)

Vix means scarcely, hardly, or with difficulty.

So vix possint means:

• can scarcely
• can hardly
• are barely able to

It adds the idea that counting the books is difficult because there are so many of them.

A useful way to hear the sentence is:

• so many books are lying on the table that the students can hardly count them

Because discipuli is the subject of possint in the ut clause.

Inside the subordinate clause:

• discipuli = the students
• eos = them
• numerare = to count
• vix possint = can scarcely

So the students are the ones who can scarcely count the books, which makes discipuli nominative plural.

The word order is flexible, but it is also quite natural Latin.

The sentence is:

• Tot libri in mensa iacent ut discipuli eos numerare vix possint.

A few things to notice:

• Tot libri is placed first, which highlights the large number immediately.
• in mensa comes before iacent, placing the location before the verb.
• In the result clause, eos numerare stays together fairly naturally.
• vix is placed near possint, where it clearly modifies the idea of being able.

Latin often uses word order for emphasis more than English does. Beginning with Tot libri makes good stylistic sense because that idea triggers the result clause.

Yes, Latin might omit it if the meaning were clear from context:

• Tot libri in mensa iacent ut discipuli numerare vix possint.

That could still be understood as so many books are lying on the table that the students can scarcely count.

However, eos is helpful because it makes the object explicit: count them. It avoids any momentary uncertainty and can add a slight emphasis on the books themselves.

The biggest clue is tot.

Latin often signals result with words like:

• tam = so
• ita / sic = so, in such a way
• adeo = to such an extent
• tantus = so great
• tot = so many

So tot libri ... ut ... strongly points to:

• there are so many books that ...

A purpose clause would usually express intention:

• He does this in order that...

But books lying on a table do not have a purpose. The clause describes the consequence of the large number of books, not the intention behind it.

Numerare is the normal Latin verb meaning to count or to number.

It is a very straightforward choice here:

• numerare libros = to count books
• eos numerare = to count them

A learner should simply recognize it as the regular verb for counting quantities one by one.

In many contexts, tot basically means so many. Depending on the situation, English might sometimes render it as this many, especially if someone is indicating a number by gesture or context. But in this sentence, because of the ut result clause, so many is clearly the right sense:

• Tot libri ... ut ... = So many books ... that ...

That pattern is a classic result construction.

The sentence divides like this:

Main clause:

• Tot libri in mensa iacent
• So many books are lying on the table

Subordinate result clause:

• ut discipuli eos numerare vix possint
• that the students can scarcely count them

This is a useful habit when reading Latin: first find the main clause, then identify what kind of subordinate clause follows.

Here is a word-by-word breakdown:

• Tot — indeclinable adjective/quantifier, so many
• libri — nominative plural masculine of liber, subject
• in — preposition
• mensa — ablative singular of mensa, object of in, expressing location
• iacent — 3rd person plural present active indicative of iacere
• ut — introduces a result clause
• discipuli — nominative plural masculine of discipulus, subject of possint
• eos — accusative plural masculine pronoun, referring to libri
• numerare — present active infinitive of numerare
• vix — adverb, scarcely / hardly
• possint — 3rd person plural present subjunctive of posse

This kind of breakdown is often the fastest way to understand how the sentence fits together.