to-infinitive&gerund

The tenses are reflected by the main verb of the sentence.Gerund and To-infinitive do not bear tenses.

2012-04-06 14:46:06 補充：
Gerund 動名詞 和 To infinitive 都不表達時態。 Gerund 也可以當名詞使用。
時態由句子的主要動詞和 ttime of adverb 反影。
例：
Jogging is a very good exercise.
'Jogging' 是 Gerund 動名詞，當名詞使用。
動詞是 “is” 表達時態是「現在式」。

Tom became strong by lifting weights.
'lifting' 是 Gerund 動名詞
動詞是 “became” 表達時態是「過去式」。

2012-04-06 14:46:27 補充：
Sue taught Amy to play badminton yesterday.
“to play ”是 to-infinitive
動詞是 “taught” 表達時態是「過去式」。
"yesterday" 是 adverb of time，要和動詞時態互相配合。

2012-04-06 15:54:29 補充：
Hi Raymond

Thank you for your comment.
I have over looked the auxillary verbs - 'have' and 'be'.

2012-04-06 15:56:11 補充：
The auxilliary verbs have (used to form the perfect) and be (used to form the pasive voice and continuous aspect).

2012-04-08 13:40:10 補充：
In general, Infinitive do not have tense, aspect, moods, and/or voice, or they are limited in the range of tenses, aspects, moods, and/or voices that they can use. (In languages where infinitives do not have moods at all, they are usually treated as being their own non-finite mood.)

2012-04-08 13:42:39 補充：
However, the auxiliary verbs have (used to form the perfect) and be (also used to form the passive voice and continuous aspect) both commonly appear in the infinitive.

Examples could be refer to Raymond's comment

2012-04-08 13:54:07 補充：
如果 “be” 的作用是被動式 (passive voice)，時態仍由句子中的主詞表達。
例： The games is going to be started.
“be started” 是被動式。時態由 is going to 表達（在未來）。

例：Infinitive can be used after the direct objects of many transitive verbs
“be”在這句子中的 infinitive. “be used” 組成passive voice。
時態是現在式因為這是“fact”； “can”表達出這句子是現在式。

2012-04-08 13:56:02 補充：
不過我們仍需留意不是出現“have” 或 “be” 便一定帶有時態。
例： He is going to be late.
“be” 在這句子裡是 infinitive ；不帶有時態。

They are goint to have dinner together.
“have” 在這句子裡是 infinitive ；不帶有時態。

2012-04-08 13:58:45 補充：
當 “be” 和 “have” 以 infinitive 的形態出現，怎樣去分別是否含有時態，就要看這兩個字後面是可有其他的動詞，和跟著 “be” 和 “have” 後面的動詞是 - present participle （例： telling等）或 past participle （例：told等）.。

To fghijh,
Infinitive (gm) is basic form of a verb such as, be or swim;,an infinitive is used by itself eg swim in:- He can swim or with to (= the to infinitive) as in he likes to swim.
Tense bears and depends on auxiliary verb+main verb to infinitive to reflect tense. eg He could have gone to swim yesterday.
---------------He could swim yesterday.

Gerund:-a present participle of a verb bears the modal verb+main verb to reflect the tense. eg.He preferred travelling than studying in Old China!.He was fond of swimming when in primary one,private school.
This gerund form of verb serving as cases of the INFINITIVE in its noun usage.
Modal verbs have only one form where they have no -ing,hence gerund has -ing.Hence the third singular form:He could speak with 3 friends then.
-------------------------------------------------He can speak 2 languages now.
He will try and visit London(tomorrow)
He could invite Susan years ago, but (could) not.
Modal verbs are ;-could,can---will,would---may,might---should,shall-----must,ought to,dare,need,----have to,used to-------
Treat gerund,infinitive as auxiliary,the English main verb determines the TENSE.

小草 ,

How about the following sentences?

The girl is believed to have told the truth.
The boy seems to be telling the truth.