Thinking Without Expression?

In Lectures On Kant’s Political Philosophy by Hannah Arendt, it is written:

“Thinking, as Kant agreed with Plato, is the silent dialogue of myself with myself , and that thinking is a “solitary business” (as Hegel once remarked) is one of the few things on which all thinkers were agreed. Also, it is of course by no means true that you need or can even hear the company of others when you happen to be busy thinking; yet, unless you can somehow communicate and expose to the test of others, either orally or in writing, whatever you may have found out when you were alone, this faculty exerted in solitude will disappear. “

From this quote, it can be inferred that thinking is a solitary activity. So in a group of people in which everybody is in a thinking state, they would be considered as performing dialogues within themselves, isolated from the others. However, the worthiness of this inner dialogue with one’s self would only come to existence when it is transferred to the outer world. It should also be noted that this activity, which proves the superiority of Man compared to other creatures, is wholly free. To further elaborate, it is not possible for an external power to intercept with this activity without causing direct physical harm to one’s neurons. It is better explained by Arendt:

So even though the activity of thinking is considered to be wholly free and independent, and since one’s dialogue with one’s self can only be unearthed by expression, it is deducible that freedom to think must coexist with freedom of expression.