I am now a gifted intervention specialist, but I taught English for 19 years on the high school level, and also taught English (writing and composition, and research paper) on the university level. And has already been stated, "thought" is the correct past tense of the verb "think."
Now, for you grammar buffs, here is a good question. I know the answer, do you?
As we know, we are taught in school about two types of verbs---action and linking. Action verbs state action whereas a linking verb is a state of being (The car is blue.) The car is in the state of being blue. Therefore "is" is a linking verb. A linking verb must have one of two things---either a predicate adjective that describes the subject "car" ("blue" was the predicate adjective in the example I gave---blue describes the car), or a predicate nominative that renames the subject, like "The car is a Ford." So that is it---either a noun renaming the subject (predicate nominative), or an adjective describing the subject (predicate adjective).
Now for the question. Tell me what type of verb this is:
The car is here.
Before you answer, realize it is not action because "is" is not an action. And before you say linking, realize that a linking verb has either a predicate nominative or a predicate adjective. The word "here" is not a noun renaming the subject "car" nor is it an adjective describing the "car." The word "here" as it used in the example is an adverb. There is no noun or adjective following the verb "is." So---what is it?
_________________
"My journey has just begun."