Through others we become ourselves.

What a child can do today with assistance, she will be able to do by herself tomorrow.

Psychology teaches us at every step that though two types of activity can have the same external manifestation, whether in origin or essence, their nature may differ most profoundly.

Language is the tool of the tools

The true direction of the development of thinking is not from the individual to the social, but from the social to the individual.

The only 'good' learning is that which is in advance of development.

It may be said that the basic characteristic of human behavior in general is that humans personally influence their relations with the environment and through that environment personally change their behavior, subjugating it to their control.