Introducing English Linguistics

to-infinitive clause, contains the base form of the verb preceded by the
infinitive marker to:
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INTRODUCING ENGLISH LINGUISTICS

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[To
choose the best model initially,] we examined main effects and inter-
action terms for the Armed Forces Qualifying Test composite. 
(ICE-USA W2A-024)
[To
begin to decrease this isolation] is therefore a vital part of the stress-
reduction programme. 
(BNC CKS 1275)
While all of the previous subordinate clauses contained non-finite verb
phrases, it is also possible for a subordinate clause to contain a finite verb
phrase and be headed by a subordinating conjunction, such as if, because,
while, who, when, and even though. In the example below, the subordinating
conjunction if heads a subordinate clause containing the verb phrase has
been discussed, which is headed by the finite verb has:
I don’t know [if that issue has been discussed by the um coordinating
council]. 
(SBCSAE)
The examples below contain additional instances of subordinate claus-
es with different subordinating conjunctions:
[When my finances are more stable] I will visit Paris. 
(ICE-GB W1B-008 135)
They had a vague idea [where the place was].
(BNC AO3 846)
They were actually selling their beadworks [because they realized a lot of
Westerners were really into that.] 
(MICASE LEL115JU090)
These actors are place entrepreneurs [who strive for maximum financial
return through investing, renting, or taxing property.] 
(ICE-USA W2A-014)
The last example above with who is a specific type of subordinate clause
known as a relative clause. Relative clauses are embedded in noun phras-
es. They begin with a relative pronoun: who(m), which, that, whose, and
(sometimes) where and when. In the above example, who is chosen because
it is used to replace a personal noun, in this case place entrepreneurs. The
relative pronoun that could also have been used:
These actors are place entrepreneurs that strive ...
That can also replace non-personal nouns along with which. In the exam-
ple below, which replaces the non-personal noun cottage:
I lived with an elderly lady in a little thatched