In 1929, Edwin Herbert Land invented a polarizing filter that was featured in a number of products, from sunglasses to...

Let's begin by understanding the meaning of this sentence. We'll use our understanding of pause points and segment the sentence as shown - understanding and assimilating the meaning of each segment bit by bit!

Sentence Structure

• In 1929,
• Edwin Herbert Land invented a polarizing filter
  • that was featured in a number of products,
    • from sunglasses to 3D movies.
• A decade later,
• Land [?] his technology
  • to invent the world's first instant camera,
    • the Polaroid Land camera.

Understanding the Meaning

The first sentence gives us background:

• 'In 1929, Edwin Herbert Land invented a polarizing filter'
  • This tells us who (Edwin Herbert Land) and what he did (invented a special filter)
• 'that was featured in a number of products, from sunglasses to 3D movies'
  • The filter was used in various products
  • We get examples: sunglasses and 3D movies

Now the second sentence moves forward in time:

• 'A decade later'
  • About ten years after 1929 - so around 1939
• 'Land ______ his technology'
  • This is where we have the blank
  • Land did something with his polarizing filter technology

Let's look at our choices. We need to fill in what Land did:

1. used
2. to have used
3. to use
4. using

Here's what we notice about the structure:

• 'Land' is the subject of the sentence
  • We need to say what action Land took
• Every sentence needs a main verb - the action word that tells us what happened
  • This verb needs to be in a form that shows when it happened (past, present, or future)
• Looking at our choices:
  • "used" - this is a complete verb form (simple past tense)
  • "to have used" - this is an infinitive form (to + verb)
  • "to use" - this is also an infinitive form
  • "using" - this is a participle form (verb + -ing)
• The key point: Infinitives (to + verb) and participles without helping verbs cannot serve as the main verb of a sentence
  • They're incomplete verb forms
  • They need other words around them to work

So we need: used - the simple past tense form that serves as the main verb.

The sentence reads: "A decade later, Land used his technology to invent the world's first instant camera, the Polaroid Land camera."

Let's verify this makes sense:

• "used" is the main action - what Land did with his technology
• "to invent" shows the PURPOSE - why he used it
• The sentence is complete and grammatically correct

Grammar Concept Applied

Finite Verbs as Main Verbs

Every complete sentence must have a finite verb - a verb form that shows tense (when the action happened) and can stand as the main action of the sentence. Infinitives and participles are non-finite forms (called this in grammar terms) that cannot serve as main verbs by themselves.

Finite verb forms (CAN be main verbs):

• Simple present: Land uses his technology
• Simple past: Land used his technology
• Future: Land will use his technology

Non-finite forms (CANNOT be main verbs alone):

• Infinitive: to use → needs a finite verb first ("Land wanted to use...")
• Participle: using → needs a helping verb ("Land was using...")

How this applies to our question:

• Subject: Land
• Needs: A finite verb showing past tense (historical context)
• "Used" = finite verb (simple past)
• "To have used" = infinitive
• "To use" = infinitive
• "Using" = participle without helping verb

The sentence structure is:

• Main action: Land used his technology (finite verb)
• Purpose: to invent the world's first instant camera (infinitive showing why)