Participium saepe ad nomen pertinet et quasi verbum et adiectivum simul continet.

Because participium is the subject of the sentence.

• participium = participle
• It is a neuter singular nominative noun.
• The verb pertinet is singular, so it matches this singular subject.

So the basic structure begins:

• Participium ... pertinet = The participle ... belongs / relates

Literally, ad nomen pertinet means pertains to a noun or belongs with a noun.

A few points:

• pertinere ad is a standard expression in Latin meaning to relate to, to belong to, or to pertain to
• ad takes the accusative, so nomen here is accusative singular
• Even though English might say belongs to a noun, Latin often uses pertinere ad rather than a dative here

So:

• ad nomen = to / with respect to a noun
• pertinet ad nomen = it pertains to a noun

In this kind of grammatical statement, singular nouns are often used in a general sense.

So nomen here means:

• a noun
• or the noun in the sense of the category noun

Latin often uses the singular for general definitions, much like English can say:

• The lion is a dangerous animal
• meaning lions in general

So ad nomen pertinet means the participle is something that goes with a noun generally, not just one specific noun.

saepe means often, and it modifies the verbal idea pertinet.

So:

• Participium saepe ad nomen pertinet = A participle often pertains to a noun

In sense, saepe applies to the whole statement that a participle is connected with a noun. It does not just describe nomen or participium by themselves.

quasi means something like:

• as if
• so to speak
• as it were
• in a sense

Here it softens or qualifies the statement. The writer is saying that a participle is not literally two separate things, but it behaves almost like both.

So:

• quasi verbum et adiectivum = as it were, a verb and an adjective

This is a very natural use of quasi in explanations and definitions.

This is a common Latin pattern for both ... and ....

So:

• et verbum et adiectivum = both a verb and an adjective

The first et introduces the first item, and the second et introduces the second item.

In this sentence, the structure is slightly expanded by quasi:

• et quasi verbum et adiectivum simul continet

That still means the participle has both verbal and adjectival character.

Because they are the direct objects of continet.

• continet = contains
• What does the participle contain?
  • verbum
  • adiectivum

So both are accusative singular:

• verbum = a verb
• adiectivum = an adjective

Latin often uses the singular here in a general or classifying sense: the participle contains the nature of verb and adjective.

simul means at the same time, simultaneously, or together.

It emphasizes that the participle has these two qualities at once:

• verbal force
• adjectival force

So:

• verbum et adiectivum simul continet = it contains a verb and an adjective at the same time

That is exactly the key grammatical idea behind a participle.

You are right that this is not meant in a physical sense. continet here is used more abstractly.

It means something like:

• includes
• combines
• embodies
• has within itself

So the idea is:

• a participle has something of the nature of a verb
• and something of the nature of an adjective

That is why a participle can:

• take tense/voice-related verbal meaning
• but also agree with a noun like an adjective

Latin word order is much more flexible than English word order because Latin uses endings to show grammatical function.

In this sentence:

• Participium is clearly the subject because it is nominative
• nomen must go with ad because ad takes the accusative
• verbum and adiectivum are objects of continet
• saepe, quasi, and simul are adverbs/particles placed for emphasis and flow

So Latin does not need to keep a rigid English-style order like:

• The participle often belongs to a noun and in a sense contains both a verb and an adjective at the same time

The actual Latin order is chosen for style and clarity, not because position alone determines function.

In grammatical Latin, adiectivum can be used as a substantive, meaning an adjective.

So here:

• adiectivum does not mean adjectival
• it means an adjective as a noun

This is very common in grammatical terminology. Latin often turns an adjective into a noun when the context makes the meaning obvious.

So:

• verbum = verb
• adiectivum = adjective

The sentence is explaining the nature of a participle.

It makes two main points:

1. A participle belongs to a noun

   • so it behaves like an adjective
   • it agrees with a noun

2. A participle also contains verbal force

   • so it behaves in some ways like a verb

That is why a participle is often described as a form that is part verb, part adjective. This sentence is essentially a compact grammatical definition of that idea.